Travi,
Ran some tests today in our labs and I was able to modify an existing message (as long as PROPAGATEATTR is set to yes since default is no) to yellow color, highlighted and non scrollable with a )MSG rule very similar to this:
MSG ***
)PROC
MSG.COLOR = OPSCOLOR('YELLOW')
MSG.DESC = OPSBITS(11)
The key point here is that if you are using the OPSLOG records to confirm changes for the route or descriptor codes they will not be there caused they are cute before the rule fires and change them.
Also another key point here is that the console you are using to display themodified messages has to support extended attributes if the color is anything other than red, white, green or yellow.
Is worth also to check if your 3270 emulator software is not replacing colors with others that might be giving you a false reading on what the console is really using.
Hope this helps Travi otherwise just cut a ticket so we can take this offline
Regards, Cesar