color: support "default" to restore fg/bg color

The name "default" can now be used in foreground or background colors, and means to use the terminal's default color, discarding any explicitly-set color without affecting the other attributes. On many modern terminals, this is not the same as specifying "white" or "black".

Although attributes could previously be cleared like "no-bold", there had not been a similar mechanism available for colors, other than a full "reset", which cannot currently be combined with post-reset settings.

Note that this is not the same as the existing name "normal", which is a no-op placeholder to permit setting the background without changing the foreground. (i.e. what is currently called "normal" might have been more descriptively named "inherit", "none", "pass" or similar).

Robert Estelle (2):
color: add missing GIT_COLOR_* white/black constants
color: support "default" to restore fg/bg color

 Documentation/config.txt | 18 +++++++++++++-----
 color.c                  | 23 ++++++++++++++++++++++-
 color.h                  | 12 ++++++++++++
 t/t4026-color.sh         | 12 ++++++++++++
 4 files changed, 59 insertions(+), 6 deletions(-)

base-commit: 225bc32a989d7a22fa6addafd4ce7dcd04675dbf
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1116%2Frwe%2Fansi-default-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1116/rwe/ansi-default-v1
Pull-Request: https://github.com/git/git/pull/1116

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