Rereading your post i realize that I skipped the part where you said you were already working on the logo.

If you are going to do the grey undersleeve, I suggest marking the arm with a shallow cut with an xacto all the way around it to mark where the sleeve will end. Unless you have a very steady hand, that is the easiest way to get the undershirt to have a crisp edge look.
But again, you don't have to do that. I could imagine that the original CN wouldn't have an undershirt. ;-)
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