I thought there should be some songs in here:

The Red Flag
The Ould Orange Flute
The Yellow Rose of Texas
The Green Fields of France (yeah, I know that's not Eric Bogles's choice of title. Tough.)
Deep Blue Sea
A bunch of violets.

I missed out Indigo, because I'm never too sure what it look like, and I don't know a song for it. (Mood Indigo doesn't count, unless it's got words I've never heard.)