Imagine you're watching a black-and-white movie on an old TV, and it looks kind of washed out. You fiddle with the contrast, and suddenly the movie looks much crisper and with better contrast. You're not actually seeing more colors -- its just grayscale -- but you can optimize it to give you more depth of perception.
That's what EnChroma does. It doesn't actually make you see red, but it heightens the contrast to make it stand out more.
https://pijul.org/