I did a little reading, and it is only a soft piece of rope or leather that loops around the horses jaw. You can attach either one or two reins. They are meant to be used hardly at all, and aren't recommended unless you horse works also completely off your legs and voice.
I've played around with doing an indian motif on Magic (since her saddle has indian designs on it, and I wanted to make her flashy for a parade), and what I decided on was this:
For feathers/beads... Get a beading hook for people (I got one at a local beauty shop for a little under $10), and follow it's instructions for beading the hair (generally they're something like string the beads onto the hook, put some hair through the loop at the end, and then push the beads upward, onto the hair. You'll have to experiment with your horse's hair, since it'll probably have a different consistency than people's hair.) Then just band the end to hold the beads in place.
For the feathers, I got some bird feathers from the old barn and slid the shaft up under the last two or three beads, then put another band over the feathers, holding them under the beads and also reinforcing the beads.
For the paint... I just went to a beauty store and bought some temporary spray on hair dye to use on the body, and I found these cow markers at the farm store that I used on her face.
As far as the war bridle.... I, personally, wouldn't suggest one. They're meant only for horses that will respond 100% of the time to voice or leg cues, with little to no use of the rein(s).
You can also use sidewalk chalk that's wet. The therapeutic barn I used to work at would have occasional days where the riders would "decorate" the horses and the chalk was always my favorite, I put a circle around their eye every time. =]