A blur (or spread filter) on the mask would probably help the forest blend a bit better.

To change the mountain colour, go into the mountain colour layer and use Colours->Hue-Saturation. This will let you shift the colours (using the hue slider) around the spectrum and decrease the colour intensity with the saturation and lightness sliders. Getting a good brown is always hard on computer screens...(at least for me...)

Nice first effort, though! Glad you found the tutorial useful.

-Rob A>