A couple thoughts. On second thought, let me grab my biology book. Brb.
I'm not sure on the overlap of colors that cones can see, but I am somewhat familiar with the general stuff, so don't expect me to be specific. I am working off my book (
conveniently pictured in the BA's blog!) so if I get it wrong it's my fault.
All photoreceptors require an two protiens to work. First is a protien that bonds to the light-absorbing pigment retinal. Retinal is a protien that is part of the light sensitive cell. The other protien is something called an opsin which bonds to the retinal, affecting its light gathering abilities.
Rods work a little differently than color cones (to follow), in that they create something called
rhodopsin. Rhodopsin, from what I understand (and I may be wrong, the book is somewhat technical here) takes on a funny property when it absorbs light. With too much light the retinal part of the rhodopsin actually seperates from the opsin, which in turn changes the shape of the opsin protien rendering it relatively ineffective. In a dark-ish environment the chemical reactions that bleach (deactivate) the opsin in light cease and the rhodopsin can form. I am not sure what the threshold is, but I would imagine it varies by species, and likely even person to person.
It takes time, 3-10 minutes for basic, functional night vision, up to 3 hours for the full amount. As far as I know, rods are not sensitive to color, but are highly sensitive to contrast. The book mentions that as well, though it was published in...I want to say 2003. Do you have a newer reference George? I'm not going to buy the next edition of a $400 book just to check if rods can see color. I would be interested if someone had a good study on rods and color.
Color vision requires cone cells (they look like cones, you can stop guessing!) and cone cells use photopsin. There are three types--green, red, and blue as mentioned in other posts. Each cone's retinal is sensitive to one of those colors, and each binds to a unique opsin to form
photopsin.
And now to quote from the book
Quote:
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"The absorption spectra for these pigments overlap, and the brain's perception of intermediate hues depends the differenetial stimulation of two or more types of cones. For example, when both red and green cones are stumulated, we may see yellow or orange, depending on which of these two populations of cones is most strongly stimulated. Color blindness...{blah blah inherited}...is due to a deficiency or absence of one or more types of photopsin."
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Taken from "Biology", Campbell and Reece, 2006. Pages 1066 and 1067. And don't slight my reference, this isn't a paper and I don't remember the specifics. Each department had their own "style" for references...oh, don't even get me started. Forget I said it.
The color part is fascinating to me...sounds an awful lot like how a computer creates colors. I'm sure it's not a pure coincedence, though I don't know the extent of any intentional design in that way. Seems like I should but it's early in the morning and I'm done thinking after this--it's the weekend!
There's a ton more, the book has several pages on the eye and vision, even outlining the chemical reactions one step at a time. It's quite fascinating, but a heck'va lot more than I care to type here. And without diagrams most of you wouldn't care to read it all anyway. Even if you did read, it would be hard to follow, so ~p->q and I'm done.