Yaaaay. Never has half an hour flown by so quickly.
Stupid SPOILER won't work:
The colours work. They actually do. I would have wished they'd put in more shadows and highlights, though - as it is now, the characters end up looking somewhat flat in some scenes (and Mokona looks weird all the time =/). They also could have let them move around a bit more, instead of just freezing when someone's talking. It's an OAV afterall, we should be able to expect a little more than from a TV series.
Enough complaining. The seiyuus all do well, and the music is awesome as usual. Overall, me likey.