Test color blindness experience with this utility

By complete coincidence, I ran into this: Color Oracle. It's a little tool that lets you modify the colors on your computer screen so that what you see is more or less what someone with color blindness would see. When you select the most common type, deuteranopia, you immediately see that the color red is indistinguishable from green or gray. However, green and red are very often used to signal "good"/"continue" versus "bad"/"stop", even on the computer.