man: Document COLORFGBG environment variable

Default colors are not contrast enough on dark backround
and this functionality, which uses more suitable colors
is hidden in the code.

Signed-off-by: Petr Vorel <pvorel@suse.cz>

diff --git a/man/man8/ip.8 b/man/man8/ip.8
index 84ade1104b48a3a6a6b6b8d3c8626d8c5d613fca..133d40d569df3403674d3b9ffb2eb5bc752d0d89 100644 (file)
--- a/man/man8/ip.8
+++ b/man/man8/ip.8
@@ -189,6 +189,12 @@ precedence. This flag is ignored if
 .B \-json
 is also given.
 
+Used color palette can be influenced by
+.BR COLORFGBG
+environment variable
+(see
+.BR ENVIRONMENT ).
+
 .TP
 .BR "\-t" , " \-timestamp"
 display current time when using monitor option.
@@ -330,6 +336,17 @@ Usually it is
 or, if the objects of this class cannot be listed,
 .BR "help" .
 
+.SH ENVIRONMENT
+.TP
+.B COLORFGBG
+If set, it's value is used for detection whether background is dark or light and use contrast colors for it.
+
+COLORFGBG environment variable usually contains either two or three
+values separated by semicolons; we want the last value in either case.
+If this value is 0-6 or 8, chose colors suitable for dark background:
+
+COLORFGBG=";0" ip -c a
+
 .SH EXIT STATUS
 Exit status is 0 if command was successful, and 1 if there is a syntax error.
 If an error was reported by the kernel exit status is 2.