webpmux: fix the -bgcolor description
@@ -85,7 +85,8 @@ Where: 'loop_count' must be in range [0, 65535].
.BI bgcolor " A,R,G,B
Set the background color of the canvas on an animated file.
.P
-Where: 'loop_count' must be in range [0, 65535].
+where: 'A', 'R', 'G' and 'B' are integers in the range 0 to 255 specifying the
+Alpha, Red, Green and Blue component values respectively.
.TP
.BI icc " file.icc
Set ICC profile.
