I did one for a friend's grandson in greens that was various designs with leaves, tiny paisleys that looked like amoebas, vines, a pinstripe, a gingham-look, a small plaid.
It came out very nice and definitely not girly. Now the one I did for his sister was very girly...pale pinks and purples tied with satin ribbon!
I vote for the polka dots. Maybe see if you can also find some white dots on blue as well.