🚀 go-pugleaf

I'm trying to make a program that will start another task that adjusts
the screen colours (yes that seems a bit much to start another task for -
just trust me :-).  The point is: I need, of cpurse, to know when this
task ends; and I think the easy way would be to have it send a message.
And the easiest way to deal with that message would be through the IDCMP
of the main window - that way there's only one port to muck with.
But I'll need a message to send...
   There's a macro in the intuition/intuition.h header LONELYMESSAGE
in the MessageClass macro setion that isn't documented anywhere.
Was this provided for this sort of application? would it be safe
(portable/ no conflicts/ etc) to use it as a class and make up a code?
Or do you have a better suggestion that can be implemente in less
than 1000 :-) lines?