diff --git a/README.md b/README.md
index 57ff142..705debe 100644
--- a/README.md
+++ b/README.md
@@ -209,7 +209,8 @@ objects. At 68 388 stars the old encoding — one JSON object per star, its eigh
 repeated each time — would have been about 17 MB to download and parse before the first frame.
 Splitting it puts the numbers in `stars.bin` (positions, handed to the GPU verbatim) and
 `stars-meta.bin` (id, magnitude, colour index, spectral-type index, the band and colour system
-those were measured in, and the distance's relative error), and leaves `stars-index.json`
+those were measured in or whether the colour was read off a temperature, and the distance's
+relative error), and leaves `stars-index.json`
 holding only the strings, with the ~2 600 distinct spectral classifications collapsed into a
 dictionary. The result is 2.6 MB for 7.8× the stars. `star-catalog.ts` defines the layout once
 and both the ETL and the app use it, so the writer and the reader cannot drift apart.
diff --git a/src/app/features/galaxy-system/star-readouts.spec.ts b/src/app/features/galaxy-system/star-readouts.spec.ts
index ced5dec..2fffbcb 100644
--- a/src/app/features/galaxy-system/star-readouts.spec.ts
+++ b/src/app/features/galaxy-system/star-readouts.spec.ts
@@ -50,6 +50,11 @@ describe('starReadouts', () => {
     expect(value(starReadouts(GAIA_STAR), 'Colour')).toBe('BP−RP 1.43');
   });
 
+  it('says a colour read off a temperature was not measured', () => {
+    const kepler445 = { ...HYG_STAR, magnitudeBand: 'G' as const, colorIndex: 1.66, colorFromTemperature: true, source: 'exoplanet-archive' };
+    expect(starReadouts(kepler445).find((readout) => readout.label === 'Colour')).toEqual({ label: 'Colour', value: 'B−V 1.66, from its temperature', derived: true });
+  });
+
   it('says a stand-in magnitude was not measured, and leaves out a colour there is none of', () => {
     const unmeasured = starReadouts({ ...GAIA_STAR, magnitude: 12, magnitudeBand: undefined, colorIndex: null, colorSystem: undefined });
     expect(value(unmeasured, 'Magnitude')).toBe('Not measured');
diff --git a/src/app/features/galaxy-system/star-readouts.ts b/src/app/features/galaxy-system/star-readouts.ts
index b601a6f..dd18ae6 100644
--- a/src/app/features/galaxy-system/star-readouts.ts
+++ b/src/app/features/galaxy-system/star-readouts.ts
@@ -44,7 +44,13 @@ export function starReadouts(star: StarRecord, surface?: StarSurface): HudReadou
     // A G magnitude and a V one are not comparable: a red dwarf is up to three brighter in G.
     { label: 'Magnitude', value: star.magnitudeBand ? `${star.magnitudeBand} ${star.magnitude.toFixed(2)}` : 'Not measured' },
     ...(star.colorIndex !== null
-      ? [{ label: 'Colour', value: `${star.colorSystem === 'BP-RP' ? 'BP−RP' : 'B−V'} ${star.colorIndex.toFixed(2)}` }]
+      ? [
+          {
+            label: 'Colour',
+            value: `${star.colorSystem === 'BP-RP' ? 'BP−RP' : 'B−V'} ${star.colorIndex.toFixed(2)}${star.colorFromTemperature ? ', from its temperature' : ''}`,
+            ...(star.colorFromTemperature ? { derived: true } : {})
+          }
+        ]
       : []),
     ...(surface?.luminositySolar
       ? [{ label: 'Luminosity', value: formatLuminosity(surface.luminositySolar), ...(surface.luminosityDerived ? { derived: true } : {}) }]
diff --git a/src/app/shared/astro/spectral.spec.ts b/src/app/shared/astro/spectral.spec.ts
index 7fcef7d..0300767 100644
--- a/src/app/shared/astro/spectral.spec.ts
+++ b/src/app/shared/astro/spectral.spec.ts
@@ -99,19 +99,22 @@ describe('spectralTypeToColorIndex', () => {
 });
 
 describe('temperatureToColorIndex', () => {
-  it("puts the Sun's temperature at its own B-V and a cool dwarf redder", () => {
+  it("puts the Sun's temperature at its own B-V and a cool dwarf where the dwarf sequence has it", () => {
     expect(temperatureToColorIndex(5772)).toBeCloseTo(0.65, 2);
-    expect(temperatureToColorIndex(3400)).toBeCloseTo(1.79, 2);
+    // Two thirds of the way from M2 (3 560 K, B−V 1.505) to M2.5 (3 470 K, 1.522).
+    expect(temperatureToColorIndex(3500)).toBeCloseTo(1.5163, 4);
   });
 
-  it('stays inside the range the spectral classes span', () => {
-    expect(temperatureToColorIndex(2566)).toBe(2);
-    expect(temperatureToColorIndex(50000)).toBe(-0.33);
+  it('reads back as the temperature it came from, so the correction is the one at that temperature', () => {
+    for (const temperatureK of [31400, 12000, 7000, 5772, 4000, 3500, 3157, 2566, 2420]) {
+      expect(dwarfSequenceAtColor(temperatureToColorIndex(temperatureK))!.temperatureK).toBeCloseTo(temperatureK, 6);
+    }
   });
 
-  it('has no answer for a temperature that is not one', () => {
-    expect(temperatureToColorIndex(0)).toBeNull();
-    expect(temperatureToColorIndex(Number.NaN)).toBeNull();
+  it('has no answer outside the table, nor for a temperature that is not one', () => {
+    for (const temperatureK of [580, 2419, 31401, 50000, 0, Number.NaN]) {
+      expect(temperatureToColorIndex(temperatureK)).toBeNull();
+    }
   });
 });
 
diff --git a/src/app/shared/astro/spectral.ts b/src/app/shared/astro/spectral.ts
index 82fa1c9..1b8362a 100644
--- a/src/app/shared/astro/spectral.ts
+++ b/src/app/shared/astro/spectral.ts
@@ -104,22 +104,23 @@ export function spectralTypeToColorIndex(spectralType: string | null | undefined
 
 /**
  * B-V colour index for an effective temperature, for stars the Exoplanet Archive gives a
- * temperature but no B magnitude. Inverts Ballesteros (2012), T = 4600 K · (1 / (0.92 (B-V) +
- * 1.7) + 1 / (0.92 (B-V) + 0.62)), a blackbody fit good to a few per cent from A to early M: it
- * puts the Sun's 5 772 K at 0.65, which is the Sun's own. Clamped to the range the class anchors
- * above span, because the fit runs on past it — TRAPPIST-1's 2 566 K would come out at 2.7.
+ * temperature but no B magnitude: the dwarf sequence below read the other way, interpolated
+ * between the two types the temperature falls between, so that the correction and the temperature
+ * read back off the colour are the table's at that temperature. Ballesteros' blackbody fit, used
+ * before, runs 0.1 to 0.2 redder than the table below 3 800 K, and the colour it gave was read on
+ * the table: 3 500 K came back as 3 102 K with a correction 1.15 magnitudes too large, and the 57
+ * hosts placed this way were off the archive's own luminosity by 0.23 dex at the median. `null`
+ * outside the table, 2 420 to 31 400 K, rather than a colour clamped to its end — CFBDSIR
+ * J145829+101343, a 580 K brown dwarf, read as B−V 2.00 and "~M6".
  */
 export function temperatureToColorIndex(temperatureK: number): number | null {
-  if (!Number.isFinite(temperatureK) || temperatureK <= 0) {
+  const [hottest, coolest] = [DWARF_SEQUENCE[0], DWARF_SEQUENCE[DWARF_SEQUENCE.length - 1]];
+  if (!(temperatureK <= hottest[3] && temperatureK >= coolest[3])) {
     return null;
   }
-  // With x = 0.92 (B-V) and k = T / 4600 the fit is k x² + (2.32 k - 2) x + (1.054 k - 2.32) = 0,
-  // whose larger root is the physical one.
-  const k = temperatureK / 4600;
-  const b = 2.32 * k - 2;
-  const c = 1.054 * k - 2.32;
-  const x = (-b + Math.sqrt(b * b - 4 * k * c)) / (2 * k);
-  return Math.min(BEYOND_M, Math.max(COLOR_INDEX_ANCHORS.O, x / 0.92));
+  const cooler = Math.max(1, DWARF_SEQUENCE.findIndex((row) => row[3] <= temperatureK));
+  const [hot, cool] = [DWARF_SEQUENCE[cooler - 1], DWARF_SEQUENCE[cooler]];
+  return hot[1] + ((cool[1] - hot[1]) * (hot[3] - temperatureK)) / (hot[3] - cool[3]);
 }
 
 /**
diff --git a/src/app/shared/models/star-catalog.spec.ts b/src/app/shared/models/star-catalog.spec.ts
index f085ce6..012d531 100644
--- a/src/app/shared/models/star-catalog.spec.ts
+++ b/src/app/shared/models/star-catalog.spec.ts
@@ -105,15 +105,18 @@ describe('the photometry and distance error columns', () => {
     { id: 3, name: 'HD 3', x: 0, y: 0, z: 300, magnitude: 7, magnitudeBand: 'V', spectralType: 'K0', colorIndex: 1.0, colorSystem: 'B-V', distanceError: 0.000001, distanceFromGaia: true, source: 'hyg' },
     { id: 4, name: 'Gaia DR3 4', x: 5, y: 5, z: 0, magnitude: 12, spectralType: 'Unknown', colorIndex: null, distanceFromGaia: true, source: 'gaia' },
     // A Hipparcos parallax smaller than its own error.
-    { id: 5, name: 'HIP 5', x: 0, y: 200, z: 0, magnitude: 6, magnitudeBand: 'V', spectralType: 'B8', colorIndex: -0.1, colorSystem: 'B-V', distanceError: 1.4, source: 'hyg' }
+    { id: 5, name: 'HIP 5', x: 0, y: 200, z: 0, magnitude: 6, magnitudeBand: 'V', spectralType: 'B8', colorIndex: -0.1, colorSystem: 'B-V', distanceError: 1.4, source: 'hyg' },
+    // An archive host whose B−V is its temperature's.
+    { id: 6, name: 'Kepler-445', x: 0, y: 0, z: 90, magnitude: 17.6, magnitudeBand: 'G', spectralType: 'M4', colorIndex: 1.66, colorSystem: 'B-V', colorFromTemperature: true, source: 'exoplanet-archive' }
   ];
   const encoded = encodeStarCatalog(MEASURED);
   const decoded = decodeStarCatalog(encoded.index, encoded.positions, encoded.meta);
 
   it('carries the band, which colour the colour index is, and whose parallax the distance is', () => {
-    expect(decoded.map((star) => star.magnitudeBand)).toEqual(['V', 'G', 'V', undefined, 'V']);
-    expect(decoded.map((star) => star.colorSystem)).toEqual(['B-V', 'BP-RP', 'B-V', undefined, 'B-V']);
-    expect(decoded.map((star) => star.distanceFromGaia)).toEqual([false, true, true, true, false]);
+    expect(decoded.map((star) => star.magnitudeBand)).toEqual(['V', 'G', 'V', undefined, 'V', 'G']);
+    expect(decoded.map((star) => star.colorSystem)).toEqual(['B-V', 'BP-RP', 'B-V', undefined, 'B-V', 'B-V']);
+    expect(decoded.map((star) => star.distanceFromGaia)).toEqual([false, true, true, true, false, false]);
+    expect(decoded.map((star) => star.colorFromTemperature)).toEqual([false, false, false, false, false, true]);
   });
 
   it('keeps a distance error to within a step at both ends of its range, and none as none', () => {
diff --git a/src/app/shared/models/star-catalog.ts b/src/app/shared/models/star-catalog.ts
index 0972a10..db850b9 100644
--- a/src/app/shared/models/star-catalog.ts
+++ b/src/app/shared/models/star-catalog.ts
@@ -44,10 +44,10 @@ export const BYTES_PER_STAR_META =
  * Bits of the photometry column. The band takes two: none (a stand-in magnitude), V or G. None
  * of it follows from the source, which records where the *position* came from: 62 002 stars
  * Gaia places keep HYG's V and B−V, and the archive's stars in G have a B−V from their
- * temperature. The last bit says whose parallax the distance is, which for a HYG star Gaia did
- * not place can still be Gaia's.
+ * temperature. The next bit says whose parallax the distance is, which for a HYG star Gaia did
+ * not place can still be Gaia's, and the last whether the colour was read off a temperature.
  */
-const PHOTOMETRY = { bandV: 1, bandG: 2, bandMask: 3, colorBpRp: 4, distanceFromGaia: 8 } as const;
+const PHOTOMETRY = { bandV: 1, bandG: 2, bandMask: 3, colorBpRp: 4, distanceFromGaia: 8, colorFromTemperature: 16 } as const;
 
 /**
  * The distance error column holds the square root of the relative error, in 255ths, and 0 where
@@ -186,7 +186,8 @@ export function encodeStarCatalog(stars: readonly StarRecord[]): {
     columns.photometry[index] =
       (star.magnitudeBand === 'V' ? PHOTOMETRY.bandV : star.magnitudeBand === 'G' ? PHOTOMETRY.bandG : 0) |
       (star.colorSystem === 'BP-RP' ? PHOTOMETRY.colorBpRp : 0) |
-      (star.distanceFromGaia ? PHOTOMETRY.distanceFromGaia : 0);
+      (star.distanceFromGaia ? PHOTOMETRY.distanceFromGaia : 0) |
+      (star.colorFromTemperature ? PHOTOMETRY.colorFromTemperature : 0);
     // At least one step, so an error too small to round to one is not read back as none published.
     columns.distanceErrors[index] =
       star.distanceError === undefined ? 0 : Math.max(1, Math.round(Math.sqrt(Math.min(1, star.distanceError)) * DISTANCE_ERROR_STEPS));
@@ -242,6 +243,7 @@ export function decodeStarCatalog(index: StarCatalogIndex, positions: Float32Arr
       colorSystem: Number.isNaN(colorIndex) ? undefined : photometry & PHOTOMETRY.colorBpRp ? 'BP-RP' : 'B-V',
       distanceError: distanceError === 0 ? undefined : (distanceError / DISTANCE_ERROR_STEPS) ** 2,
       distanceFromGaia: (photometry & PHOTOMETRY.distanceFromGaia) !== 0,
+      colorFromTemperature: (photometry & PHOTOMETRY.colorFromTemperature) !== 0,
       ...(source ? { source: source.id } : {})
     };
   }
diff --git a/src/app/shared/models/star.model.ts b/src/app/shared/models/star.model.ts
index 392c281..43ee7ff 100644
--- a/src/app/shared/models/star.model.ts
+++ b/src/app/shared/models/star.model.ts
@@ -33,6 +33,11 @@ export interface StarRecord {
    * Mamajek). Absent with it.
    */
   colorSystem?: 'B-V' | 'BP-RP';
+  /**
+   * Whether `colorIndex` was read off the dwarf sequence at the star's effective temperature rather
+   * than measured: the 57 archive-placed hosts with a temperature and no B magnitude.
+   */
+  colorFromTemperature?: boolean;
   /**
    * Relative uncertainty of the distance, σd/d: the relative error of the parallax it was
    * inverted from, which to first order is the same — or, for a star the Exoplanet Archive places,
diff --git a/src/assets/data/stars-meta.bin b/src/assets/data/stars-meta.bin
index c3e0e8e..6d4fb64 100644
Binary files a/src/assets/data/stars-meta.bin and b/src/assets/data/stars-meta.bin differ
diff --git a/tools/etl/build.ts b/tools/etl/build.ts
index 6b89d7d..00aca0b 100644
--- a/tools/etl/build.ts
+++ b/tools/etl/build.ts
@@ -74,7 +74,10 @@ function validateStars(stars: StarRecord[]): void {
     assertCondition(decoded[i].spectralType === stars[i].spectralType, `Star catalogue round-trip lost the spectral type of star ${stars[i].id}.`);
     assertCondition(decoded[i].colorIndex === null === (stars[i].colorIndex === null), `Star catalogue round-trip changed whether star ${stars[i].id} has a colour index.`);
     assertCondition(
-      decoded[i].magnitudeBand === stars[i].magnitudeBand && decoded[i].colorSystem === stars[i].colorSystem && decoded[i].distanceFromGaia === !!stars[i].distanceFromGaia,
+      decoded[i].magnitudeBand === stars[i].magnitudeBand &&
+        decoded[i].colorSystem === stars[i].colorSystem &&
+        decoded[i].distanceFromGaia === !!stars[i].distanceFromGaia &&
+        decoded[i].colorFromTemperature === !!stars[i].colorFromTemperature,
       `Star catalogue round-trip changed the photometry of star ${stars[i].id}.`
     );
     // Stored as its square root in 255ths, up to 100 %; see `star-catalog.ts`.
diff --git a/tools/etl/fetchExoplanets.ts b/tools/etl/fetchExoplanets.ts
index 7d1f1c0..6400b8f 100644
--- a/tools/etl/fetchExoplanets.ts
+++ b/tools/etl/fetchExoplanets.ts
@@ -170,6 +170,7 @@ export async function fetchExoplanets(stars?: StarRecord[]): Promise<{ exoplanet
           spectralType: compositeRow?.['st_spectype'] || 'Unknown',
           colorIndex,
           ...(colorIndex === null ? {} : { colorSystem: 'B-V' as const }),
+          ...(colorIndex !== null && (b === undefined || v === undefined) ? { colorFromTemperature: true } : {}),
           ...(above === undefined || below === undefined ? {} : { distanceError: (Math.abs(above) + Math.abs(below)) / 2 / distancePc }),
           source: ARCHIVE_SOURCE
         };