judykay

Whatever design you decide to use I would use variegated thread with so many colors in the piano keys. Just my opinion but I use variegated thread for hand quilting a lot on table runners.

Sewze

For my very first quilt (not knowing what I was doing) I put piano keys on the borders and using a variegated thread I went on an upward angle from the bottom to the inner narrow border and then down the next key....like an inverted "V".... I think it looks very nice and it was simple to do.

Holice

There are two suggestions for design other than SID that I might consider.
One is a design (stencil) of music lines and notes that could be quilted in the border. Another is a continuous line stars border that might work. Both these are available from the on line stencil companies.