Health wise there is no difference between the color of the betta (unless it's a true black (melano) female, then it is likely sterile). There has been some debate I've seen on several other forums that in males, the darker colors are often considered more aggressive in temperament, and thereby blues are often more dominant over reds if placed in the same tank.
Aside from a couple videos of different people keeping two male bettas (one red, one blue) in a tank together and the blue one always being the aggressor who chased the red one around (which I always thought was a terribly stupid idea to begin with, sticking two males in the same tank), there was never any real proof offered other than it might lie with the theory that in the wild the dakrer betta is often the healthier betta, and is thereby generally more fit and able to beat the other betta.
In terms of more succeptible to any diesease though? No, I don't know of any color that is more likely than another to fall ill.