All budgies fall into one of two basic varieties. Either they have a yellow pigment base or they lack a yellow pigment base and are therefore white-based. In general, the base color is visible in the mask feathers and between the black stripes of the head and wings. (The exception is the yellow-face variety.) Normally, the body feathers are structured to reflect blue. In yellow-based budgies the blue in the body feathers combines with the yellow base pigment, which results in a bright green, the most common variety. In white-based budgies there is no yellow base pigment, so the blue structure of the body feathers results in bright blue coloration.

Basic Genetics:
Yellow-base - dominant
White-base - recessive
Details on base color genetics...

A yellow-based budgie results in the classic green variety.	A white-based budgie results in the common blue variety.

Click Here to see more photos comparing the above mutations