So you have the Red-Green-Blue cables? Are you sure you have them plugged into the correct plugs? There are two different types of cables for the iPad:
Red-Yellow-White composite cables and Red-Green-Blue component cables. Make sure you are plugging into the correct plugs. In other words, you can't plug RGB component into RYW plugs.
Also, try it with the video app instead (play a movie that you have on your iPad, not through Youtube). I know for a fact that works if you have it plugged in correctly because I tried it out.
