Here are some (kind of half-arsed) natural Dye recipes. I have included a basic 'rule of thumb' recipe, and have tried to supply a good representation of as many of the colours as I can here. The brown to yellow range is the easiest to obtain. Blue and black seem to be the rarest of colours, with indigo, woad, and some mushrooms being able to produce suitable blues, and logwood or sometimes purple loosestrife being used for black.

The Basic Recipe-This will work for many plants.
-Pre-mordant fiber. All these recipes arre for 8 oz (220 g) fiber.
-Extract dye-Soak your plant material, deepending on how hard it is, for up to 24 hours.
Boil plant materials for 20 minutes, barks/shells/roots-30 min, until dye has been extracted, and there is not much colour left in the material. If the dye has not all been extracted, pour dye liquor off, add more water, and heat again. You may have to do this a few times with barks etc.
-Strain out plant material.
-If necessary, add enough water for the ffiber to be able to move freely in the dye bath
-Add wetted fiber to the dye, and simmer for about 1 hour, or longer if a deeper colour is needed. If using Iron or Tin as a post-mordant, add now and simmer 10-20 minutes more.
Use this basic recipe for most of your dyeing, and unless otherwise stated

Okay, specifics, as per the dye book:

Plant Material-400g Onion Skin
Mordant- Alum with Ammonia rinse
Colour-orange Iron yields dark brown chrome is reddish brown
Special Instructions-You may rinse this after dyeing in an ammonia rinse of 2 tbsp ammonia to 2 ga (8l) of water. Make sure the rinse is about the same temperature as the bath.

Plant Material- 200g marigold flowers-or 150 g dried flowers
Mordant- Alum
Colour-bright yellow to gold Rust with chrome

Plant Material-450g Purple Loosestrife-tops (when flowering), stems
Mordant-Iron
Colour-Black (but I�ve never done this-illegal here)
Special Instructions-Use unmordanted fiber. Add to dye bath, and soak over night. Reheat the dye bath to simmering. Remove fiber and add enough Iron to turn the bath a dark black colour. Return fiber to dye bath and simmer until a deep black is obtained. This will take at least an hour.

Plant Material-3 tbsp Powdered Henna Leaves
Mordant-Tin and 100g Cream of tartar
Colour-rust

Plant Material-3 tbsp Tumeric Spice
Mordant-vinegar or lemon juice
Colour-Yellow

Plant Material-Lilac Leaves
Mordant-Alum and Cream of Tartar
Colour-Yellow-green

Plant Material- Crushed Acorns
Mordant- Alum
Colour-yellow stone with Iron-green stone with alum/iron brown gray with chrome/iron strong gray

Plant Material-Chicory
Mordant- Alum
Colour-Mustard yellow with Iron forest green Adding peppermint will create different shades of green

Plant Material-Ground Lichen
Mordant-none
Colour-Tan-Brown, though different varieties, through fermentation, will give different colour. Special Instructions-Lichen is hard to remove from fibers and yarns. For this reason, you don�t want it to come into contact with your fiber. Layer lichen on bottom of an enamel canner. Cover with a layer of double cheese cloth or thin cotton. Add the fiber, then another layer of cheese cloth. Repeat these steps, ending with a lichen layer. Pour enough water to cover everything. Put lid on the pot and simmer for an hour and a half or longer. If this is too much work, you can also place your lichen in a cheese cloth bag.

Plant Material-200 g Bloodroot
Mordant-Alum
Colour-red