All of the "do we want color" flags default to -1 to indicate that we don't have any color configured. This value is handled in one of two ways:
1. In porcelain, we check early on whether the value is still -1 after reading the config, and set it to the value of color.ui (which defaults to 0).
2. In plumbing, it stays untouched as -1, and want_color defaults it to off.
This works fine, but means that every porcelain has to check and reassign its color flag. Now that want_color gives us a place to put this check in a single spot, we can do that, simplifying the calling code.
Signed-off-by: Jeff King <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>