The first thing coming to mind is going with the red for the patriotic theme, if your quilt dreamland is in the USA. LOL
I know you said you want the next fabric to be all the same, but being a scrappy quilter, I can't help thinking how good your quilt would look if the third color was also scrappy but controlled to a color range. If you are going for a batik, I'd try to find one with a good variation of color tones, probably in greens with a little rust and white for a cooler color palette.
For a warmer feel I'd probably go with either a blend of red,orange,yellow blend batik, or the yellow, white, with a touch of orange/red or green, but not both. Can't wait to see what you decide to do.

I like Jan's idea of using yellow, yellow-orange and orange if using blenders. But what I'd really use is a very dark, navy batik with splashes of bright colors in it---I have a piece my stash right now that is almost navy and has small dots, in a rainbow progression, of yellow, pink, green, purple that would be perfect.