Linked from
The 13 pages that link to Opsin, each with the reason it gives.
Color visionRelated: How each opsin's absorption spectrum is tuned decides what its cone detects.
TrichromacyRelated: Small opsin differences separate the three cone classes' peak sensitivities.
AchromatopsiaRelated: Cone opsins provide wavelength sensitivity in ordinary color vision.
TetrachromacyRelated: Differences in cone opsins can produce distinct wavelength sensitivities.
Simple eyeRelated: Opsins detect photons in the photoreceptor cells of many simple eyes.