provide --color option for all ref-filter users

When ref-filter learned about want_color() in 11b087adfd
(ref-filter: consult want_color() before emitting colors,
2017-07-13), it became useful to be able to turn colors off
and on for specific commands. For git-branch, you can do so
with --color/--no-color.

But for git-for-each-ref and git-tag, the other users of
ref-filter, you have no option except to tweak the
"color.ui" config setting. Let's give both of these commands
the usual color command-line options.

This is a bit more obvious as a method for overriding the
config. And it also prepares us for the behavior of "always"
changing (so that we are still left with a way of forcing
color when our output goes to a non-terminal).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-for-each-ref.txt

@@ -55,6 +55,11 @@ OPTIONS
 	literally, in the latter case matching completely or from the
 	beginning up to a slash.
 
+--color[=<when>]:
+	Respect any colors specified in the `--format` option. The
+	`<when>` field must be one of `always`, `never`, or `auto` (if
+	`<when>` is absent, behave as if `always` was given).
+
 --shell::
 --perl::
 --python::

Documentation/git-tag.txt

@@ -115,6 +115,11 @@ options for details.
 	variable if it exists, or lexicographic order otherwise. See
 	linkgit:git-config[1].
 
+--color[=<when>]:
+	Respect any colors specified in the `--format` option. The
+	`<when>` field must be one of `always`, `never`, or `auto` (if
+	`<when>` is absent, behave as if `always` was given).
+
 -i::
 --ignore-case::
 	Sorting and filtering tags are case insensitive.