While that's true Jerry (& I've been know to teach graphic arts consultants), there are three things we're concerned with about the target. (1) The background, (2) the foreground, and (3) the eventual bullet holes. They need to contrast one with the others.
And as one who has a good shooting buddy who is color blind -- red & green wind flags don't help him so much -- that's an area where a medical consultant might be of use. My color blind friend is why my flags are solid red on one side, and striped black & white on the other. I have no idea about what target colors would help or hurt him -- and I think there are different forms of color-blindess, aren't there?
For cheapest costs, we want only two colors on the targets. Just which those two should be could use some study.
BTW, I agree with you on the heavier bull. Aside from just being able to see it when things aren't so good, there's another use. I've used it to gauge mirage (hence air movement) during conditions like you sometimes find in Match 1 -- there isn't much air, but the dot on the scope will move from the inside to the outside of the ring, so you know it's there. And when you have to lay down a small one -- as everyone is trying to do with match 1, that helps. For me, this takes the heavy ring -- the puny rings are too thin.