I love all your fabrics except the light brown .You are right that it doesn't work, and the reason is that almost all of your colors are cool. Brown is neutral but feels/reads warm. The black sets off the cool tones. I would audition a shade of purple (like your magenta flower) or a blue that matches the blue flowers. I'm leaning toward blue since you have the fewest blue flowers in the print--it would bring out that blue and look vibrant against the black and your rainbowish border.