Git format-patch viewer?

I found a solution:

cat patch | colordiff | less -RS

Further reading: http://www.markusbe.com/2009/12/how-to-read-a-patch-or-diff-and-understand-its-structure-to-apply-it-manually/ (archived copy)

I've made a tool to view diff side-by-side: https://app.box.com/s/l8rmp281aptq711fqwve

Screenshot:

Now it was updated to v0.4 to support file list.

Source code: https://github.com/megatops/PatchViewer