I encountered this problem in my jCaster where I can't take a screenshot when running fullscreen - all I get is black image. Fraps handles the situation slightly better, but still colors are a bit off (like blue-ish?). I guess it has to do with how gosu renders graphics, but in other projects it works fine (i used texplay with this one, does it matter?) so why is this even an issue?

BTW here's the Fraps output:
http://imgur.com/a/BIRCw