Oh what FUN your quilt is!
Borders? You've got a lot going on in the centre of the quilt, and to me, unless you find an absolutely "right" border fabric, it could draw away from the showpiece of each block in the quilt. That being said, if I were shopping for a border fabric, I would look for a multicolour thin stripe featuring the black and other colours. However, the chances of finding the "right" one, are probably very slim.
Sooooo ... If you're good to go with it as is ... then star binding it!
For me, I'd go with the same black as your sashings ... IF you have enough.
IMHO the black would frame it all up nicely ...
and not distract from the JOY in each of the blocks!