Paint side of cake.
Make cake paint following formula provided (4 drops blue base color + 2 drops pink base color + 3 drops black base color + 4 to 5 drops water). Using fine-tip brush, paint small plus signs in five to six groups at base of cake. Paint small upward strokes above plus signs. Let set about five minutes.
Using slightly dampened wide flat brush, brush over upward strokes, pulling color up towards top of cake. Let set about five minutes.
Using fine-tip brush and white-white icing color, paint upward strokes over blue strokes.