There are different types and degrees of color blindness. So, what one color blind person can't see, another may be able to see perfectly fine.
The absolute safest bet is black and white. But, the general rule of thumb is to use colors that are high contrast in terms of light and dark (ergo, black and white).
A color-blind person may or may not be able to see red or green. But, you can use red or green and be more mindful of color-blind people if you go with different degrees of lightness and darkness. So, even though someone might not be able to see red (for instance), they could still ascertain a difference between a pinkish color and a dark red.
Here's a nifty article that might help: http://www.somersault1824.com/tips-for-designing-scientific-figures-for-color-blind-readers/