I have a 12" round cake in the oven right now for birthday girl today. here is the theme of the party.

http://www.partycity.com/product/neon+doodle+party+supplies.do?sortby=ourPicks&pp=60&size=all&navSet=169767

She wants all buttercream details but i don't know how to get the "tie dye" effect on the cake. should i draw freehand on the cake or would it be better to do a frozen buttercream transfer?

thanks a lot for your help!