I'm often surprised by how many visual designers don't take color blindness into account for their designs. I have a mild form of red/green color blindness myself; usually I only have difficulties telling certain colors apart, requiring a second or third look, but today I encountered a particularly striking example where I literally could not distinguish some colors.
The following image is from the game Dynetzzle, level 9:
Note that each field is marked on at least one side by a colored bar, and that there are three colors used on the left side of fields, grayish magenta as well as light brilliant gamboge and moderate olive.
The latter two are completely indistinguishable to me in-game; I can see a difference when they're put next to each other, but it's not large enough for me to be able discriminate small patches that have a certain distance between them.
Of course, it's obvious even to me that the colors are different if you darken the image:
I used this image as a reference in order to solve this level, but I couldn't help but think that this shouldn't be necessary. When you create a design, no matter whether it's a game, presentation, chart, diagram etc., that uses color to convey information of any kind, please, do not solely rely on color; also use hatchings, shapes, or something similar so that color-blind people won't get tripped up.
Oh, and as for Dynetzzle — it's a great game, so check it out. The only other complaint I have is that it's not longer!