I have also seen many people use a neutral whole cloth (purchased or hand made) as the bedspread, then use any size quilt they like over the top. You can turn a small square throw on point, or fold a larger quilt and place it at the foot for a runner. This way you can add a splash of color without having to make a quilt to fit the whole bed.
FF covered the size quilt a frame can accommodate, but you can always have the main 'body' of the quilt and the drops quilted separately then join them using a QAYG technique after.