@ MarjoryWarrenne:
http://www.cloverflowers.com/custom/TutPage002.html
How to Dye a My Little Pony
These are just two dye tutorials out there; there are plenty more to choose from, I'm sure. I think the current recommendation is to give your pony the vinegar wash right after dyeing to prevent fading, and then to let her sit for [as long as you can handle it] some time after that. In my personal experience the pony does tend to go through an initial fade and then settle into her color over the course of several months, so I tend to dye them a bit darker than the color I actually want. But that is just my personal experience. You'll want a warm color bait (like orange) for warm dye colors and a cool color bait (like blue) for cool dye colors. I've heard that dyeing ponies in very dark colors like black can come out...unfortunate...so you might want to do a FBR on those; I haven't tried black myself.