Use duct tape for words. Place crayons on top. Blow dry on high heat till crayons melt. Blow dry side to side to blend colors. Slowly remove duct tape to reveal words. I've seen the crayon thing before, but love the duct tape idea!
Melted Rainbow Crayon Art Tutorial - by Glorious Treats.make this, but don't glue the crayons on. Either make the rainbow colors cover the entire canvas, or put verse in place of crayons. I've always wanted to make one of these!