U is for UTEE Marbled Background. I found this technique on Wendy's blog, she has a couple more UTEE background techniques in that same post.
Cover a thin piece of cardboard with embossing or VersaMark ink. Cover with black UTEE and heat set with a heat tool. Repeat two more times, so you have three layers of embossing enamel covering the cardboard. I did try to coat the thin cardboard by dipping it in black UTEE that was melted in a melt pot, but that gave too thick of an application.