Fix typo in manual

i3lock.1

@@ -89,7 +89,7 @@ Display the given PNG image instead of a blank screen.
 
 .TP
 .BI \-c\  rrggbb \fR,\ \fB\-\-color= rrggbb
-Turn the screen into the given color instead of white. Color must be given in 6-byte
+Turn the screen into the given color instead of white. Color must be given in 3-byte
 format: rrggbb (i.e. ff0000 is red).
 
 .TP