Try setting git.color.diff.meta, e.g.

git config --global git.color.diff.meta blue

or by manually editing the configuration file

[color "diff"]
    meta = blue

I am not aware of any official list of these settings, but many blogs have mostly complete unofficial listings.

Try setting color.diff.meta, e.g.

git config --global color.diff.meta blue

or by manually editing the configuration file

[color "diff"]
    meta = blue

You can look through the various color. settings in the git-config reference for more possible settings. The color.diff.meta setting is listed here:

color.diff.<slot>
Use customized color for diff colorization. <slot> specifies which part of the patch to use the specified color, and is one of plain (context text), meta (metainformation), frag (hunk header), func (function in hunk header), old (removed lines), new (added lines), commit (commit headers), or whitespace (highlighting whitespace errors). The values of these variables may be specified as in color.branch.<slot>.