The background is a technique I call "Speckled Watercolor Wash Background." Not sure if that's an official technique name, but it fits for what I did. I used my Spectrum Aqua Markers to paint with.
Doesn't that background look like one of those giant jaw breakers? Like an explosion of yummy on paper! I applied a wash of light blue to the watercolor cardstock panel. After it dried (Confession: I dried it with my heat gun..cause I was impatient!) I flicked other colors on...making sure each color was dry before moving on to the next.
The Spectrum Aqua Marker used for the watercolored background: