An interesting idea Jack. The only problem would be getting musicians to agree on the colour of a key -- I have known fierce arguments to break out on this subject.
But you could widen the scheme perhaps by using the colours of the rainbow and the jazz chord system:
Red         I
Orange II
Yellow   III
Green    IV
Blue       V
Indigo    VI
Violet    VII

Then you'd have a book that could be played by anyone in any key.