I'd probably use a batik blue and batik green. They come in fabulous deep and bright colors, plus there is just enough texture in the fabrics to make them interesting. Hancock's of Paducah online has a good selection. Hoffman Bali Watercolor Solids are a line of batiks that are not solid. Here are a couple of possibilities for blue and green:
http://www.hancocks-paducah.com/SHOP...r-Solid-Brooke
http://www.hancocks-paducah.com/Hoff...or-SNAKE-GREEN
For a two-color quilt, it's best to go to a quilt shop so you can see the actual fabrics side-by-side.
Edit: Or order swatches. Some online shops have a way for you to do that.