Just as ArnimS said, currenly you can use various video filters in mplayer though I can't advise anything to manipulate them at runtime. Also filters introduce additional cpu load and can make video unwatchable. If you are converting video anyway, you can try to use some filters to change colors at the conversion stage.

By the way, Nokia 770 graphics chip has some support for gamma correction in hardware, though I'm not sure if this functionality is supported in the current version of Nokia 770 framebuffer driver.

Here is a link to epson mobile graphics chip documentation for those who may be interested:
http://www.erd.epson.com/index.php?o...d=36&Itemid=40