Color coding is really nothing new--radio component manufacturers started doing it in the 1920s. However, color coding of audio cables is an area that's sometimes overlooked.
In the days before stereo, multitrack and timecode, it didn't really matter. Black or grey went well with everything.
Color coding became useful with the advent of SMPTE timecode. This very fast rise-time signal required careful handling to prevent it from bleeding into program audio. To create an awareness of the potential for timecode crosstalk, at least one plant began installing yellow-jacketed cable for timecode runs. (Yellow equals caution!)
Other colors could be used to identify other signal types: non-dropframe SMPTE timecode for clocks could get orange; white for channel one; red, channel two, etc.
At present, most manufacturers offer a somewhat limited range of jacket colors for AES/EBU 110-ohm cable, but unless you're running a lot of tiers, these are sufficient for making digital feeds stand out from the pack.
Cable color coding can even be worked into patch-panel labeling and CAD drawings. If red-jacketed cable is used for channel two audio, it's easy to create patch-panel labels with red text for channel two I/Os, and to use red lines for channel two on drawings.
There are many benefits for color coding. Without referring to drawings or look-up tables, anyone can identify an audio signal type and be certain that correct connections are made to equipment when it's returned from maintenance. When punching down a large number of audio runs, it's impossible to accidentally connect the wrong channel to a patch panel--misplaced cables really stand out. Also, it's a no-brainer to realize that you're about to patch a channel two output into a channel one input.
It's also very convenient to be able to identify a signal type without digging into stacks of drawings and cable run sheets.
