Feature: Color for chords

I'd like the ability to use color in chord charts. This would help both in live play and in study. Four modes come to mind:

* Encoding color within chord source text, for new charts that I create
* Annotating color within existing charts (e.g. flag that Dbmaj7 in red)
* Automatically coloring chords by name (all Db chords in red) or family (all altered chords in blue)
* Automatically coloring of progressions (all II-V cadences in green)

The automatic coloring, especially of progressions, could be difficult but this could be a semi-automated process, where the user flags progressions manually or the app calls up certain phrases ("is this a II-VI-V?")