I've only ever seen scripts, etc for Client Access, but you do have a couple of things you can do.
First option is to create a source member called "colour" or something and then use a file editor, e.g. WRKDBF, etc, which to edit the member. The important thing is that the file editor allows you to enter in "hex" mode.
Add records with the hex codes for the colour attributes you want and then use SEU to copy and overlay these records in the source member you want highlighting. This method works best for highlighting comments in RPG programs, for example, where you can put the code in column 8 for all records.
If you don't have a file editor you can write a quick program to create the source member.
If it's RPG code you want highlighting specifically - different colours for condition statements, variables, etc - sort of like the PC based IDE's - then there is a tool RPG Alive (www.rpgalive.com) which does on the fly code highlighting. I installed it at a previous job around 5-6 years ago and it was about #1000 for a site licence. Not sure what the price is these days, but it's well worth the investment.
Hope it helps
However you do it, it's wrong. Hex codes are not valid in source members nor should they be entered.
Sooner or later, you will need to process those source members on a different system. Perhaps you'll have a development LPAR or perhaps you'll use a decent PC editor such as WDSC or RDi which will do it automatically for you. It <b>will</b> happen.
When it does, you are not going to want to clean up all of your source members to find and remove all of the control codes that never should have been there. Sending various hex codes in network transmissions can really mess things up, especially when they're not supposed to be there.