photoshop 7
create a new greyscale image and fill the background with black
Use the paintbrush tool (opacity 100%, strength 100%), pick white, and do a rough sketch of your design.
Choose the smudge tool (Mode Normal, Strength 67%). Now, just start pushing from inside to the white towards the black. Also, push the black up into the white, Pull your different grays around to create depth. Takes some practice, but it starts coming natural after a few minutes. Kinda like sculpting clay...
Now, go to Image, select Mode, and set back to RGB
Go to Image, select Adjustments, and click on Color Balance. From here, you can change the hue of the image.
Good luck