As a matter of fact, when creating the V4 default theme, Mr White Tie even specifically called upon people having color blindness of some kind to take part testing. Imho, good designers targeting the biggest possible common user base (as default is) will take this physical limitation into consideration wherever they can and will see fit. It will not solve every color issue some of us have. There are many different kinds of color deficiencies like hopi said, targeting them all might mean black and white only, not good. Also, it just makes sense to make it first and foremost appealing to people with normal vision, and people with deficiencies will have to adjust as they will in everyday life too. But yes, every program which tries to appeal to the biggest possible audience, could well have this taken into consideration too. And certainly not show important decisions just as color differences, if at all possible. If almost 10% of population has color blindness (95% of them the red-green), the number is pretty big.