Thanks for the comments guys.

LonewandererD: I saw in your post in Tear's tut that you were having problems with the forest. Hmm, well the forest layer is very dependent on what is below it. It gets most of its colour from the grass, land and elevation layers.
So first thing I'd look at was the grass layer. Paint on your mask to make sure it is a uniform colour such as solid white. If you have darker or lighter spots on your mask then it will show through as lighter and darker colour on your forests.
Your land colour layer has an influence on your grass colour so if you've altered that at all (like I did for my mountain colour) then that could alter the shade under forests.
The elevation layer gives you the general undulations of the land and has a bevel on it so any under your forest will cause shadows and light spots, so try painting on the mask in black to get rid of all elevations under the forest if you don't want this.
Umm, not sure what else to say. My settings on my forest are completely the same as Tear's tutorial directs me to have.

Edit: Oh, and of course make sure you don't have light and dark spots on your forest mask.