@sxa From the xclock man page:
BUGS
Xclock believes the system clock.
(I suspect defaulting to colour is a distro or user thing. With no customizations whatsoever, building from source gives me monochrome. I can get the colour version by running xclock -xrm '*customization: -color', although that option isn't available for xclock on Solaris 10 by the look of it. Still, that xrm setting will give you coloured apps if there's a color app-defaults file installed.)