rfe: git-config: lack of color reset option

Hi,

given the following config:

[color "diff"]
	commit = bold white blue
[color "decorate"]
	branch = green

The attributes from color.diff.commit are inherited for color.decorate.

1. There seems to be no way to reset the attributes such that
"color.decorate.branch = default green blue" wouuld have an effect.

2. It would be nice if there was an option to only paint the 
commit hash, rather than the entire line including the decorate 
parenthesis group.

(My current version is 1.7.7, but there seem to be no changes regarding color config in 1.7.8 and 1.7.9 in the release notes, so I presume the issue is still current.)