Melt candy. Melt blue, lavender, pink, green, white, yellow and turquoise candy in decorating bags, separately, according to package directions.
On waxed paper-covered cake board, pipe rainbow arches (first pink, followed by yellow, green, turquoise and lavender), about 2½ in. wide. Let set, about 3 to 5 minutes.
Using melted white candy, pipe several dots on either end of rainbow arch. Let set, about 2 minutes. Pipe more dots on top of the first to create 3D clouds. Chill until set, about 5 minutes.