I really love the look of the black, I don't feel it makes your gorgeous blocks look somber at all. I would choose to do the black all in one fabric though, maybe a batik? So many blacks have green tones or brown tones, isn't it great we all have our different reasons for our choices. Lovely project so far! I know alot of modern quilters are using the white these days, but with all those gorgeous bright colours you might have one errant one bleed, so would chose the black.