Nicely sketched. I'm gonna assume its the resolution makes it look worse than it is. As for the shirt color, its probably best in the future to just choose about 3 colors you think work really well with the shirt. Just putting them all there takes from the design and I would guess threadless likes people to be much more decisive. Id go with denim on this one.
Yeah, the resolution is normally a lot better. I usually pick only a handful of shirt colors but it was late when I submitted it and thought variety might be cool with this one. Thanks for the feedback :-)