It's beautiful. I'd use black border but some other colors in there too.
Some have suggested using a small piano key type border (1-2") plus then black. That's what I'd do.
But whatever you do would be nice. Just use black...not gray or something subtle. You've not been subtle with the colors up til now, so why would you start now at the border stage?
Anyway, did you sew down the black strips first down the middle of the block and then added the other strips?
I think it is beautiful too, and I'm saving your picture in my folder of quilts...:)