Quoting PipSqueak's Mommy:" I'm assuming it's one of those rubber-ish curtains in which case most paint will flake off. You could ... [snip!] ... off. You could paint the side of the sheet that's against the curtain and it should show through (unless it's really thick)."
Quoting Deborah B.:" it may show through but i cant tell for like 4 hours lol.. its a really think cheap dollar store curtain.. ... [snip!] ... put them on the floor and let him finger paint but i bout a art easel for a Christmas gift so i wanted to do something special."Hopefully it will, it's a really cute idea. If not here is an ehow about painting plastic that may help you out: http://www.ehow.com/how_4500402_paint-plastic.html