how big is the quilt? the picture makes it look huge! i don't think a piano key border would really compliment it- it is a totally different look- if it needs a border (to finish the edges or to bring it to a larger size i would stick with a narrow white one...or maybe a wider white one (depending on how much i need to add to make it the size i wanted it to be. any color you choose is going to (draw out) that color in the quilts- so if you used the light blue- all of the light blue blocks would (Pop) out...same with any other color- so if you want to showcase a particular color in it that would be the way to do it- if you wanted people to look at it & think of it as a purple quilt- you would use purple in the border- which would bring all of the purples out...
it is beautiful-
if you wanted to use all of the colors of the quilt in a border i would use the small 9-patches that are in the quilt- you could alternate them with white squares- or make long lines of them-with a narrow white on either side of the pieced row...