I believe it would be based on the standards of the company issuing the drawings. Are you utilizing National Cad Standards (NCS) or other drafting standard?
I'll take a look at the NCS and see if it has anything in there for the layers as they have pretty particular requirements.
EDIT - Looked at the NCS and found that as long as the layer is properly named, it can be any color you desire. They do not have any color limitations; only naming conventions. Sorry, I won't be of any further assistance.
Most plans I've seen use red for deletions and either green or blue for changes and additions. My logic suggests green for additions and blue for changes. At the end of the work, a complete and accurate set of as-builts should exist with no additions/changes/deletions and color should be used for the various systems. BTW, yellow is annoying to see on a print-out.