Hexachromatic

He considers that color is conveyed to the mind through a perceptive centre, and that this centre is only able to distinguish six definite points of difference (colors) in the spectrum. Therefore, for normal sight, he holds a hexachromatic theory of color-vision which is independent of light and shade.

Dr. Edridge-Green has classified colour-blind people according to whether they can perceive sis colours, five, four, three, two, or only one colour. Thus, one who distinguishes all six colours, or a hexachromatic person, may be considered as normal.

It is worth noting that in 1891 Dr. Edridge-Green, of St. John’s College, put forward the view, in his Colour Blindness, p. 103, that whereas normal vision is hexachromatic, there are persons who emphatically distinguish seven colours in the spectrum, exactly as did Newton—or rather the assistant on whom Newton always relied.

Most of us, they assert, are “hexachromatic”. We see red, orange, yellow, green, blue, and violet.

“Hexachromats” have normal color vision apart from their difficulty in discriminating indigo. “Heptachromats” are faultless color perceivers. The “hexachromatic” category is assumed to be the largest.

I think that some turtles potentially have hexachromatic vision due to different matches between expressed pigment and associated oil droplet!

The scale contains 493 separate sensations, which are structurally hexachromatic and visually colourless.

If a subject with normal (trichromatic) color vision wears the glasses in Fig. 8.24, his vision will be hexachromatic (six-color).