Natural Dyes

I am a high school senior and I am doing a project on natural ways to make dyes. I would like to know the plants used to make blue, black, yellow, and purple.

There are many herbs that can be used to produce these colours. According to Rita Buchanan's book, "A Dyer's Garden" (available from Richters), some dyeplants are: yellow bedstraw (tops, yellow; roots, purple-red); black walnut (hulls, brownish black); dyers broom (tops, yellow); burdock (leaves, yellow); golden marguerite (flowers, yellow-orange); coreopsis (flowers, yellow-gold); curled dock (roots and leaves, yellow); indigo (tops, blue); madder (roots, reddish purple); marigold (flowers, yellow-orange); safflower (flowers, yellow-orange); weld (leaves, yellow); woad (young leaves, blue).
Much depends on the mordant used and the fabric dyed. For more information please consult Buchanan's book.