Dark factors affects the base colour of the bird no matter it’s mutation. Not all birds carry dark factors.
In budgerigars that are lacking color showing (as in albino and lutino) the dark factor mayl exist but will be hidden visually.
Here we will review only the Blue Series, we also have another FAQ dedicated to the Green Series
Which is abbreviated with the letters: dd, Dd or DD. Or with the numbers 0, 1, 2
dd / 0 = No dark factors appear as sky blue or light green
Dd / 1 = Single dark factor appears as cobalt or dark green
DD / 2 = Double dark factors appear as mauve or olive
All three variations have white and black stripes that wave their way over the wings and back. The differences lie in body and tail colors.
SKYBLUE - No Dark Factor - dd
A blue (white-based) budgie with no dark factor is called sky blue.
The body color of the Skyblue is bright. The tail feathers of the Skyblue are bluish black
Below is a Dominant Opaline Skyblue Hen
COBALT Single dark factor - Dd A blue (white-based) budgie with 1 dark factor is called a Cobalt.
The Cobalt's body comes in a deep cobalt blue and is much darker than the Skyblue. The tail of the Cobalt is also darker than that of the skyblue.
Below is a Cobalt Greywing
MAUVES Double dark factors DD Are a deep Blue Gray color. The Mauve variation has a mauve colored body and an even darker tail than that of the Skyblue or Cobalt