`diff --color=auto` is nice, but `vimdiff` is superior
diff -u a.txt b.txt | colordiffI use the following config.
[core]
pager = /usr/share/git-core/contrib/diff-highlight | less
[color "diff-highlight"]
oldNormal = red
oldHighlight = 16 bold red
newNormal = green
newHighlight = 16 bold green