Question

Is there a difference in muscle tone between the dominant forearm and the other forearm?

This would depend on how much each arm is used or exercised. If the person greatly favors the <I>either</I> arm, that arm would have more "muscle tone." In exercising, many people exercise both arms equally. This source might help a little.

http://www.members.cox.net/dagershaw/lol/Handedness.html

I hope this helps. Thanks for asking.