I'm not colorblind, but I feel like this is a much better way of looking at it/explaining it. Sorry if it's not. So humans have three cones to see colors, red, green and blue. Everything we see is just a mixture of them. (When you shine light through different layers of colored plastic, you get the color between the two. More layers of one specific plastic leads to a shift towards that color though.) With colorblind people, the cones overlap slightly, meaning that you can see the wrong mixture of two colors. (Usually red and green.) This means that rather than having less colored pencils, you're missing a few and you're using random spare pencils in their places. The glasses just block out those sections of the spectrum, so your brain picks whatever is closest. (That's why the glasses make some colors harder to tell apart.) Back to the pencil metaphor, the spares are just taken away and you have to pick the next best one for each situation.