Historically, a flag needed to have a few important attributes:
Be instantly recognizable on the battlefield
Be able to fly from a pole (it's why flags pretty much universally have at least one flat edge)
Be able to produce relatively cheaply (simple designs with a few colors are much easier to produce than flags with lots of parts and fancy embroidery).
A somewhat less important attribute is recognizable by various types of color blindness.
Flags also tend to inherit features from their progenitor flags (the British flag, for example, is a couple of flags mashed together). http://quizwithderan.blogspot.com/20...-of-world.html has an interesting map that shows flags attached to their countries. Similar areas may have similar flags, and former colonies may have flags very similar to their parent empire.
If the black field is part of the flag then I don't think it's a bad design. It's similar in some respects to the Japanese rising sun flag, except red and green on a black field instead of red on a white field. If the black field isn't part of the design, then I'm not sure hot to attach that flag to a standard...