Which color of light does indigo dye mostly absorb from white light?

Answer: Orange light

Blue light — No. A blue-looking dye does not mainly absorb blue light; if it did, blue would be missing from the light it sends back, so it would look yellow-orange rather than blue. Indigo looks blue because its molecule removes a different band and leaves blue-purple light. The everyday name \"blue dye\" describes the color you see, not the color being absorbed.

Orange light ✓ — Yes. In white light, indigo's chromophore absorbs most strongly in the orange region, so orange is subtracted and the remaining light reaching your eye is biased toward blue-purple. The dye is subtractive: it does not add blue light, it removes its complementary color. That is why indigo cloth and dye appear blue even though the absorbed band is orange.

Violet light — No. Violet is close to the color name \"indigo,\" so it is tempting to assume the dye absorbs violet, but that is a name association rather than the main absorption band. If violet were mostly removed, the reflected light would shift toward yellow-green, not the blue-purple we see. Indigo appears blue because orange-region light is absorbed more strongly.