Are there any open source sprite format?

PNG just plainly sucks. I has no support for animations, timing or delta compression and sequence names. Also, PNG is slow at random access (you have to decompress image before use). Proprietary formats (like Diablo 2 DCC) are much better, but highly specialized for their games: some have no true color, other have no directions.

>>35
Hell, what am I saying, you don't even need pixel shaders for coloring, you can just use the fixed function pipeline and set up some colored lighting parameters in the texture stage.