A week ago at GenCon we received some great feedback from a couple players that were color blind. They recommended that we adjust our card graphics to accommodate players that couldn't differentiate colors very well and add texture and shapes to our designs to make them easier to identify.
Our game Land of Zion is very dependent on colors since you're using resource cards based on the seven elements used in the game (wind, fire, earth, water, darkness, light, and neutral). You can find the changes below in an example we put together. We feel that the changes make each element easier to identify even in black and white by the texture and shape of each design.