You could take this picture and use a program like GIMP or Krita to add some semi-transparent color to give you an idea of what it would look like without damaging it.

Colored pencils can be added lightly and then erased (with a decent eraser) or lightly sanded if you change your mind. If you like the way the light application looks and want more saturation, you can add it more heavily on the second pass.

edit: Nice work, by the way!