Colors.color_name() no longer returns #rrggbb colors

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2065

Reported by Jonas Wallden jonasw@roxen.com

Pike 7.0:

> Colors.color_name( ({ 11, 22, 33 }) );
Result: "#0b1621"

Pike 7.2:

> Colors.color_name( ({ 11, 22, 33 }) );
Result: "-"

Is this intentional? It breaks the color selectors in base_server/wizard.pike.