You should convey important information in multiple modes, not just color. If you are still required to do so, at the very least you should complement that info with other modes, like symbols, if the user requested differentiation without color.

There are some cards from the game UNO. In that game a user throws a card based on the number or color of the card played by the previous player. A game like this could check if shouldDifferentiateWithoutColor is on to add symbols to the cards. UNO has a version of the game that uses the color blind alphabet to represent each color.