logansi,
you sit in a darkened room about 2-3m away from an old wooden box that shines two tiny dots of light at you. The colours change from red, white and yellow in random patterns and you have to say what colour they are.
It's akin to looking across Port Philip Bay at the navigation markers on the horizon and guessing the colours - that's the game my siblings used to like to play in my youth on poor old colour-blind me. IMO, if you're CVD, it's worth studying and identifying lights in this type of situation as practice, especially if you grew up knowing you are CVD. I think some of the lack of colour facility is learned through "giving up early" because "you're colour-blind, aren't you?"