My idea for a flag
The first one is the official images/symbols/colors for sol-re-sol.
I prefer the 2nd or 3rd.
The reason being is that all the symbols can be made with one hand but in the first example \ can get confused with /, especially when you are watching some one else and it is reversed.
But this would change how Jean Francois Sudre envisioned it. See chart at end of article here. SOLRESOL, THE UNIVERSAL MUSICAL LANGUAGE by by PAUL COLLINS
I can live with the 4th or 5th one. Changing sol to so and si to ti, in my opinion, should be the only change, for now.
(Do you like how the do re me fa so la ti gradually move toward the top of each box).
Also, I am liking the following more and more