I have a condition called monochromatism. The old term for it is color blindness, and I prefer the other term, not for any PC "Please don't stigmatize me" reason, but because color "blind" is incorrect. I have fewer red-green sensing cells on my retina than most people, hence I have difficulty making out different tones of those colors or colors based on them. Its not all that bad when you don't know what you are missing, and the space on my retinas was taken up by light sensing cells. So I can see the brightness of colors better than most of my friends, and my night vision seems better as well.
A note to teachers: if you have a student (typically male) who makes a lot of marks on the back of the coloring assignment while working with the big can of unlabeled crayons, recommend to their parents that they take their child for an eye exam. I certainly did that, especially since I couldn't see the red that separated purple from blue.
Speaking of teachers, I have to say that I feel for them when parents are asking them not to use red pens because the color is too stressful for children. More like too stressful for the parents remembering their school days. Let me just lay it out: the small stress that a child feels when they see that they have gotten an answer wrong should be a goad to getting the answer correct next time (you know, its called "learning") and the enhanced sense of satisfaction that comes from doing something hard. The short form is then the children will learn how to go about finding self-esteem for themselves rather than waiting for someone to come along and give it to them. Now that I think about it, someone else giving another self-esteem seems to be an oxymoron.
So maybe I'm just being my monochromatic self, but I think our kids can learn to handle a little red on their homework. Especially when they learn to get less and less red as time goes on.