Yes, you need a color to 'cool' down your hot colors. Maybe one of the lighter pinks I see in the lower right hand center as an inside border, or the turquoise, then strips of the colors you've already used. I wouldn't use an applique on that quilt even if I did do applique, which I don't! I can't imagine adding brown fabric to it.
Let us know what you finally decide, and the results.