The in-laws must be cleaning out their garage. The children brought home a huge box of highlighters. So I started thinking, "What could one do with so many highlighters?" Then I remembered Clement Hall room 308 at the University of Tennessee in Knoxville. That was my room. The walls were the color of an 80s computer that had been used too long. Dingy. Gray. Like a light but wet modeling clay. And the walls were cinder block.
A fun trick for the frequent traveler who stays in hotels a lot is to leave a message on the bathroom mirror using a light application of chap stick or other oil. Done correctly, the message remains invisible until a hot shower steams the mirror.
Highlighters on cinder block painted in that gray color work the same. Draw the highlighter art by turning off the normal lights and turning on black lights. The art in room 308 was quite intricate when my friends and I were done. When the black lights are turned off and the normal lights turned on, the highlighter disappears. Turn the black lights on and feel like you stepped into a Jimmy Hendrix black light poster.