One of our members, Incog, asked for some help on how to color rocks and mountains in the forum. In one of his examples, he showed how he did his coloring and in turn, I showed him my own technique.
So, using the base he made, I continued on and did the following using only two tools: Smudge and Blur. These two tools looks as follows:
On a side note, you should never color your original work in such a small scale. It is better to start at a large canvas size and later reduce the image file (Image > Image Size/Scale Image) at a later date if you need to.
Also, you can use Smudge and Blur for other things as well aside from coloring rocks. Give it a whirl!