How do I change DiffMerge's color choices?

We routinely use Remote Desktop to control other servers.  With the new
DiffMerge, "inserted" text is green-on-green and completely unviewable
over remote desktop.  I have tried various resolution settings on the
remote desktop, but none seem to help.  The only way I can actually SEE
the inserted lines are to select them with the mouse.

Clearly, I realize the problem is probably with Remote Desktop, but more
importantly, I seem unable to change this color scheme (which would seem
pretty important, especially considering green-on-green is going to
cause all sorts of accessibility issues).

Any thoughts, ideas?