This background began as a simple Color Halftone filter. It gradually evolved into this candy-ish look which might suggest "Birthday Cake frosting" if you live in the U.S. For those elsewhere, that would just be a white icing with colored sprinkles mixed into it. I've never eaten it, but the colors always draw my attention when I'm shopping. So...

Shown smaller than the original completed size of 2070 X 3510 pixels.

See one original source here.