BY NO MEANS! It did, in truth, begin life as a humble pale hunk of mere styrofoam.
Get some black acrylic. Thin it in water. Why acrylic? Because enamel and oil are sticky and smell bad and hard to thin and because tempera flakes right off and gouache is just expensive tempera and ink and watercolor are just for people who don't know that acrylic is cheaper and does the same thing if you thin it down.
Remember: Do all this in a clean, dry area--or not, you could just do it on your 80-year old hardwood floor. Fuck it, it's acrylic, cleans up with water.
It might kinda look wrong at first, just add lotsa paint and lotsa water, it'll settle...
So, yeah, ReduceReUseRecycleDumpsterDive all that good stuff and pretty soon you'll have an insane looking dungeon and your players will be like Wow where did you get the idea for that 3-tiered-arena? and you can be all It came to me on a vision quest in the desert instead of saying it's actually just the negative space around a coffee maker.