There aren't enough themes that take advantage of the full resolution of the Y1, and the 240p version of Rockbox is fine but themes on it look kind of bad on the 480x360 dispolay. Here's a heavily modified port of a theme I found and liked.
Original author: K4sum1
Improvements/Bug Fixes: OlsroFR
Innioasis Y1 360p Port: AkikoKumagara
Fonts Contained:
Cantarell Bold
Ubuntu Medium (Unused)