Does Nom Lumb get a stress token when rotates his firing arc due bis ability??

First off Nom's ability is not an action, just a direction to rotate.

Even if it was an action, the default color of an action is white if it is not specified. This is covered in the Rules Reference v1.2.0 page 3 in the Actions section, third diamond under "Actions have the colors..."

Edit: I just saw this was already answered in the duplicate thread.