Oooh, oooh...stencil the pink breast cancer thingy on your horse's bum!!
I just use regular sparkly glue pens, I don't spend the outrageous amounts on the 'horsey specific' stuff. I get the stuff that's able to come out with water and soap. SOOOO much cheaper, and you can get so many more colors for the price of one packet, compared to one tube/bottle of the fancy stuff, for the same price.
I also use that easily curled party 'foil' stuff for mane plaiting, and some of that sparkly wire type stuff and braid that in to the top of the tail (french braid the top, like hunter braid).
If your horse doesn't mind, you could put those Huge sun glasses you can find on him too...it's great for kicks and giggles hahahahaha