I’ve met quite a few designers who are colourblind, but personally it affects my ability to distinguish between green and brown, or blue and purple. Tones and colour strength I can see, but certain colours are hard to tell apart.
You might already know I originally trained as a wildlife illustrator. I knew which colours to use by the helpful names on the paint tubes, and even the more obscure names like Oxide of Chromium were memorable (it’s the best base for natural greens by the way). Then when I transitioned to print design, I used the CMYK system. Even if I couldn’t differentiate colours, I knew how to create, for example, a bright red numerically. Especially as the way the colours were built up was simliar to using watercolour. It was logical.