From the CloneMasters Guide To The Planet:
"Typically Clones are perfect copies of each other based on a simple genetic code, but sometimes there are mutations. The known mutations are as follows:
Light Clone - The Light Clone seems to have a small centralized brain consisting of 5-10 neurons which is just enough to stop them from walking around aimlessly. You can directly control this Clone's movement and direction as well as command them to jump.
Dark Clone - Being the most common of all mutations, the Dark Clone has superior motor control allowing them to Mold twice as fast, fall safely from any height, and triple the size of their Nova event horizon! Most impressive is that the Dark Clone can disintegrate Clonium when going Nova!"
Use the arrow keys on the keyboard to move a light clone. In the editor you can make a pre-placed clone light or dark by changing it's "Style" option.