I don't know about upsetting the loli gods or whatever. But I think if you want to be recognizable as the Joker you are right in that you need to stick with the classic color scheme. Having a "bang" gun or a friend dressed as a loli Harley with you would help too. Actually I think I'd rather see a loli Harley with an ega Joker(but then I like that cause it's similar to what a friend of mine did: http://images.cosplay.com/showphoto.php?photo=831829)
, or just a whole group of loli DC villians, cause groups always make design variations more recognizable.