While I'm not a big fan of presentation slides for speakers, I know that into each life some PowerPoint must fall. So here's a useful site, Vischeck, which checks your slides (or other visual work) to make sure that color-blind people can actually see it. From the website:
Many pictures, documents and web pages are hard for color blind people to read because the people who designed them didn't think about the problem. Vischeck lets them check their work for color blind visibility. It is also interesting to anyone who is just plain curious about what the world looks like if you're color blind.One in 20 people have some form of color blindness, and the problem is most acute with shades of red and green, so think of this as a way of ensuring that your audience has a fighting chance to pay attention to your slides. A related part of the site, Daltonize, corrects for color blindness. A hat tip to Casey Wright, who passed this resource along on Twitter.