Regular watercolors work very well if you brush the plate first with Gum Arabic.
Let the Gum Arabic dry first. Also let the watercolors dry before
trying to pull the print. Dampen paper. Best results are achieved with
an press - but you can also pull prints by rubbing the back of paper
with a spoon. Get some Karan D'ache (sp?) watercolor crayons too.
Experiment. You will like the results.