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 Green 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

Green Series
All three varieties possess purple cheek patches and yellow masks. Like the Blue Budgie they all possess throat spots consisting of three black spots on both sides of the throat. All three varieties have light yellow wings and green bodies. The differences lie in the coloring of the body plumage.

LIGHT GREEN - No Dark Factor - dd The body color of the Light Green is bright. The tail feathers of the Light Green are bluish black  Pictured below - Light Green Dominant Pied Opaline Hen

DARK GREEN Single dark factor - Dd A Green (Yellow-based) budgie with 1 dark factor is called a Dark Green. The Dark Green body comes in a deep Green and is much darker than the Light Green. The tail of the Dark Green is also darker than that of the Light Green Pictured Below - Normal Dark Green Cock

OLIVE GREEN Double dark factors DD The Olive body comes in a deep Olive Green and is much darker than the Dark Green. Olives have dark blue/purple cheek patches and black-blue tails. Pictured below: Normal Olive Hen

Review Green Show Standards read this article Standard Requirement, For A Lt Green, Dk Green Or Olive Bird.