Black first ... about 2 or 3"
Then use all your leftovers, join randomly together in 1-1/2" to 2" squares (all the same size)
Black again about 3 or 4"
I'm just giving you some approx sizes ... you need to audition this with your quilt and find the sizes that work.
The first black will frame it up.
The multi colour narrower border will pull some of the colour to the outside, and not detract from the work of the main part.
The final black just frames it all up more!