Well, seems like an old feature request that I actually like, so I would like to bump this. It was rejected on
p/672273, but that doesn't matter, that was taiko and taiko was originally designed to work for colorblind people as well.
What people don't think about is: Colorblind newbie comes to play the game and will find out it is difficult for him and colors simply blend all together. The thing is you are basically telling these people to edit skin.ini, requiring them to make own skin or download one, but let's admit it, people are lazy and newbies will get completely frustrated. What these people need is a quick solution without needing to customize the skin, they just want to play and enjoy the game.
Here, I want to show a difference between real view and approximately colorblind human for 3 different colors. The thing is that as color changes, its contrast changes as well for colorblind people, so it is hard for them to distinguish it from other colors, therefore playing with black background doesn't always help, but the solution could be just simply modifier which would allow you to change all values of RGB at once. Let's say we have 100,150,200, so increase by, say 10% would result in 110,165,220, making the color just lighter, which makes it much easier to distinguish.
That is relatively not a big deal, because it is hard to read for both, but it could still be improved for both colorblind and 'normal' people.
Fixed easily by increasing the lighting of the color.
While red for 'normal' people is pretty easy to read, for colorblind people, this looks like a complete disaster, because it converts to somewhat dark yellow, which is impossible to read on black - imagining there would be any background, some cases must be a complete killer. Obviously, it doesn't look unplayable, but imagining this in motion can be very annoying. The 3rd approach circle is literally invisible, giving a very big disadvantage, so I think ability to increase color's brightness would be absolutely easy and good solution.