You can buy colored stains to add to it, or add raw material colorants
such as red iron oxide (brown or green), copper carbonate (green), cobalt
carbonate (blue). To get a strong color it can take up to 15 % of the
colorant, but you'll have to experiment to find the correct amount.
There are some slip colorant suggestions on my writing page, the article
on feathering, I think.
Brad Sondahl--
For original art, music, pottery, and literature, visit my homepage
http://sondahl.com
Pottery sales page http://sondahl.freeyellow.com
My music site at mp3.com http://www.mp3.com/stations/sondahl