I agree, keep his colors but add in a little of another color----red is classic but turquoise, yellow, lime or orange would be fun too---just to break up the monotony,

Ditto to keeping to his black and grey decor. It could become very dramatic and help you stretch outside your safety zone!

If adding another colour, use a blacker tone of the colour, so it doesn't jump out of the mix and dominate. Quilterella's is a great example.

Extra thought here ... a colour with a black nothing print on top of it.

I am in the process of making a Day & night for my 14 yo stepson.

Split Nine Patch would be a good one too.

A lot of the boys now are going towards the camo fabric. I comes in all different color variations.

Do a search here and on Google for two-color quilts and see what comes up.

Maybe show him a few samples to see what he likes/dislikes. Tonals and batiks may catch his eye too.
The males in my family prefer nothing floral or girly LOL :D:D:D

Check out this quilt posted in another thread. A great "male" quilt and fits your colour requirements!

http://www.quiltingboard.com/t-112953-1.htm

I was just at Hancock's Fabrics today and saw some cowboy fabric in their clean sweep section. There was a tossed cowboys fabric and one with larger pictures of cowboys, mostly on horseback. The background was a deep blue and the pictures looked kind of vintage. It was only $1/yd!