Tammy: Assuming I knew what I was doing at the time . . .
I did start out going by eye color, before I realized that I was going to run into repetitions in a hurry. Then I began to get creative, and discovered I’d get repetitions anyway. That’s when I came up with no visibility for magic in the Circle universe (unless special magics are applied).
Roger’s Gift comes from the non-Conté side of his family, which is where he gets his dominant magic. It turned color in LIONESS RAMPANT through mixing with Thom’s, and after corruption by Roger’s hate and paranoia.
I try to have magical colors run in families (which is why I explain Roger’s color as I do), but it won’t always work out like that. It is why Neal’s and Baird’s colors are green, though.
And since I know my own magical system and I know a lot of our world’s theories of magic and color, it’s possible what I knew seeped into my subconscious thinking as I worked. If that’s the case, there’s a perfectly reasonable explanation for Onua’s Gift being red (other than that it’s her favorite color): red is also a protective color, and that’s what Onua can do best with her Gift, particularly when the protection involves concealment. I think having an abusive husband helped her hone that skill.
I suspect that Numair’s Gift was actually something like a deep amber or gold when he was small, his mother’s family’s Gifts being in the yellow range, his father’s in the red range, but mom’s being the dominant, but in Numair’s case it was the development and expansion of his power with each year that changed his power’s color.
I imagine Duke Gareth’s Gift was originally a dark rose in color, but as he’s aged and his heart’s gotten worse, the color has paled. He doesn’t use it any more because of the strain it would put on him, but I bet it would be light pink!