Color vision deficiency (color-blind), in humans is the inability to perceive differences between some or all colors that other people can distinguish.
It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals. (see wikipedia article for more info)
According to the medical studies, eight to ten percent of male population suffers from some kind of color blindness (figure for female population is much lower). What does it mean to the average Swing developer? Well, if you rely too much on color differences, you may be not conveying the information as well as you thought. Now you can run your application in debug UI mode and have a live preview of your UI as viewed by the color-blind population