Index: colorize.tcl
===================================================================
--- colorize.tcl	(revisione 8297)
+++ colorize.tcl	(copia locale)
@@ -32,6 +32,9 @@
 		set g [expr $g+$darken]
 		set b [expr $b+$darken]
 	    }
+	    if {$r < 0} {set r 0}
+	    if {$g < 0} {set g 0}
+	    if {$b < 0} {set b 0}
 	    set color [format "%02x%02x%02x" $r $g $b]
 	    plugins_log "Colorize" "new color: $color"
 	} else {