Andy,
The CTCParts.com web site has an introduction to CTC - see . Specifically, "Part 5: The Control Machine", at the bottom of the page, gives basic descriptions of the lamps and levers.
One thing I'm learning is that a given lever or lamp on the prototypical machine doesn't always have a simple explanation. There's always an exception. And railroad "X" did it this way but "Y" did it a different way and "Z" left that feature out and railroad "W" did something altogether different.
So, if you want to be strictly accurate-to-prototype, you need to discuss your implementation with an expert in signalling. I know that Mike at CTCparts.com is willing (eager?) to discuss, the various prototype railroad practices, including whys and what-fors, indocator colors, control machine plate shapes, sounds, signal aspects, braking distances, switch geometries, etc., and how they come together as a prototypical signal system. Getting some of his time, however, can be challenging.
Regards,
Billybob
