Not at all, that is entirely up to you.
The qubes comes in white to four "sides", that is the walls on either side, the top, and the bottom of the qube.
You're welcome to decorate these "sides" and the glass at the back too (but that may obstruct the view by shoppers who may choose to look through the qubes from within the store/kiosk).
However, if you'd rather have it clean and simplistic with the focus on the products, you're welcome to keep the walls white.
