I have some confusions about this that I'm not finding clear answers for. First, looking at the color violet, it looks like a sort of "purple". The answer as I've understood it to why the sky doesn't appear violet or this "purple" is that it has to do with a combination of the fact that there isn't as much violet produced by the sun and it's absorbed higher in the atmosphere. In addition to that is while violet appears sort of purple since it stimulates the blue cones and the red cones less, the net effect from the different frequencies of light coming into our eye is that the blue cones are stimulated most. So we see the sky as blue. What's confusing to me is that while thinking of violet as sort of a purple, I've come across some explanations that regard violet as a deep blue, not this "purplish" color. To add to this, if you look at a spectrum produced by a prism, it doesn't appear to show violet as this "purple" but a deep blue, however when you look at a rainbow you can see violet as this sort of purple. So I'm not sure what violet is actually perceived as. If violet is perceived as a purple, why doesn't this show up with a prism? If violet is perceived as a deep blue, why do we see "purple" where violet should be in a rainbow? Which is it?