[Q] should "color.*.<slot> = normal" emit nothing?

If you wanted to paint the HEAD decoration as the same color as the
body text (primarily because cyan is too faint on a black-on-white
terminal to be readable) you would not want to say

    [color "decorate"]
        head = black

because that you would not be able to reuse same configuration on
a white-on-black terminal.  I would naively expect

    [color "decorate"]
        head = normal

to work, but it does not.  I notice that we have these definitions
in color.h:

    #define GIT_COLOR_NORMAL        ""
    #define GIT_COLOR_RESET         "\033[m"
    #define GIT_COLOR_BOLD          "\033[1m"
    #define GIT_COLOR_RED           "\033[31m"
    #define GIT_COLOR_GREEN         "\033[32m"
    ...

As a workaround, I ended up doing this:

    [color "decorate"]
        head = reset

which should work OK.  But I have a feeling that the definition of
our "normal" may want to do the "reset", not "no-op" like we
currently do.

Comments?