Use different diff tool such as P4merge http://git-scm.com/book/fr/v1/Personnalisation-de-Git-Configuration-de-Git http://www.perforce.com/product/components/perforce-visual-merge-and-diff-tools (freeware)
From this video: http://opendesign.foundation/articles/designers-can-open-source-session-video/
How can designers be more open source:
Make “credit” the core reward for contributing.
Roadblocks:
“An interface to Git for graphic designers”