A blue moon is simply when two full moons occur in the same calendar month. They occur once every two to three years. There isn't any special color.
Model NIKON D200
ExposureTime 1/250
FocalLength 300.0mm
Aperture 8.0
ISO 250
Flash No Flash
ExposureCompensation +1/3
Lens 0mm f/0
LensType MF