First, a tale from Sweden. Once upon a time, the local authorities in the immigrant-dominated neighborhood of Tensta in Stockholm ordered a huge mural showing a “world tree” and flags of various foreign nations. They wanted to include a Roma (Gypsy) flag, as well, and therefore asked a local Roma group whether such a flag existed and if so, how it looks like. The local Roma had no idea, but came up with an ingenious proposal: why not a green flag with a horse and a carriage, symbolizing the traditionally nomadic nature of Gypsies? Said and done, such a flag was promptly added to the mural. The problem, of course, is that a *real* Roma flag does exist. When the artists learned about it, they promptly repainted the fictitious flag with the official one, which I personally regret since the faux design would have been a great tourist attraction (or something).
I don't know how widely used the Gypsy banner really is, but it's not unknown, and the design is interesting. The blue stands for heaven, the green for earth and the spoked wheel for the nomadic traditions of the Roma. The wheel is also reminiscent of the “chakra” shown in the national flag of India. The original homeland of the Roma was probably Punjab or Rajasthan. According to a Buddhist website, the 16 spokes originally symbolized the Eighthfold Path of Buddhism plus the eighth geographical directions. However, this is not mentioned on any Roma websites, hardly surprising since few (if any) Roma are Buddhists.
As an interesting aside, the Roma flag on the Tensta mural has a white wheel in the center, while the “official” version has a red ditto. However, I think I have seen the white-wheeled version in non-Tensta contexts, so it could be a legitimate variant.