There is a black fabric that would work well with flat, bright colours...I don't know the name but it's the most popular black at our quilt shop. On the bolt it looks like there is blue and green mottled lightly through it. What it does though is look like a rich black when put beside a colour....it makes the coloured fabric just pop.
It also gives the quilt top depth and you don't notice that the coloured fabrics are just a plain colour.
Unfortunately I don't know the name of the black, it's just the go to black we all like to use.