Cuckoo

Color and pattern male

Plumage: each feather is on gray-black ground color, three or four times slightly arched transversely interrupted by a light gray pattern, which is not sharply defined.

Ornamental feathers: the number of cross-bands is larger in proportion to the length of the feather. In those feathers, but most in the neck- and saddle-hackle, the pattern tends towards an inverted V.  Some white at the base of the tail is permitted, provided it is not obtrusively visible from the outside. 

Pure/impure: cuckoo pattern can be present both in pure breeding and impure breeding.

- In a pure breeding male the lighter bands are bright gray-white and clearly wider than the dark gray bands, overall impression is light in color.

- In a impure breeding male the lighter bands are gray-white and are clearly narrower than the dark gray bands, overall impression is similar to the color and pattern of the female.

Both pattern variants pure breeding and impure breeding are permitted.

Down: light, without  pattern.                                                                                                                                   

Note

The cuckoo pattern must be bright and as even as possible over the entire body.

Serious faults

- Purebred male: sickles and/or large steering-feathers mostly white; completely mis-colored feathers; strong yellow or rusty brown tint in the ornamental feathers.

- Impurebred male: white in tail and/or wings; too little cuckoo pattern in wings, tail and breast; completely mis-colored feathers; strong yellow or rusty brown tint in the ornamental feathers.

Faults

A few mis-colored feather-parts. A clear striping in the down feathers.

Color and pattern female

Plumage is generally colored and patterned like the male, but appears darker because the light grey cross-bands on the female are slightly narrower than the dark grey bands. 

Serious faults

Too little shaft stripe pattern. Too little cuckoo pattern in the neck-hackle. White in the wings of young chickens. Too little cuckoo pattern in wings and tail.

Faults

Slightly too light or slightly too dark color. A few off-colored feather-sections. A clear striping in the down feathers. 

Genetic code: https://kippenjungle.nl/Overzicht.htm

Website with all available information regarding chicken genetics including the chicken color calculator.