I've just started collecting fabric for my grown son's quilt. I am making a Hunter Star pattern in Batiks of Med-Dark Blues/Greens with the stars of bright yellow/orange (he LOVES orange). There are many nice "gender neutral" batiks out there. Geometric, Abstract, etc. I try not to pick anything flowery, but will use leafy prints or vines. Hoffman 1895's come in many colors and can blend in with just about anything else you use.
I think neutrals with accents in another color, like blue, burgundy, dark purple, etc. would be very nice.