pager: config variable pager.color

enable/disable colored output when the pager is in use

Signed-off-by: Matthias Lederhofer <matled@gmx.net>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/diff.c b/diff.c
index 6a71376..607c357 100644
--- a/diff.c
+++ b/diff.c
@@ -175,7 +175,7 @@
 			diff_use_color_default = 1; /* bool */
 		else if (!strcasecmp(value, "auto")) {
 			diff_use_color_default = 0;
-			if (isatty(1) || pager_in_use) {
+			if (isatty(1) || (pager_in_use && pager_use_color)) {
 				char *term = getenv("TERM");
 				if (term && strcmp(term, "dumb"))
 					diff_use_color_default = 1;