I've painted my Harook up in a variety of colours for tailfeathers and coxcombs/head feathers to give them each a bit of individuality, and I've come up with a bit of nonsense in the way of background to support the idea.
In the particular universe this bunch of agressive, willfully destructive bunch of chickenoids hail from, their natural feather colouring is a dirty off white, yellowish colour, a bit paler than their skin tones. At some time as they pass from juvenile to adulthood the Harook decides on a colour for their head gear and tail feathers and they dye them appropriately. The colour they pick is dependant on many factors, although the most predominant is the colours of individuals they admire or wish to emulate.
The tail feathers tend not to be same colouring as the coxcombs, the colouring of the coxcombs is chosen for logical (well as logical as a demented, murderous chicken can get) reasons while the tailfeathers are chosen for emotional reasons. However there are exceptions to this, as well as some individuals who chose not to dye either their coxcombs and/or tail feathers. There is also a growing naturalist movement who feel the need to pick fights on everyone else.
Human anthropologists have likened the system to the system of chariot racing in ancient rome, with the supporters following the various coloured factions. Needless to say the Harook took offence to this and the next group of visiting human scientists were pecked to death.
There are no set colours, and a Harook could chose to pick any colour regardless of what other Harook choose, however the colours currently prevailant in Harook society are red, purple, light and dark blue, green and yellow. Harook also vary the shade of the base colour according to some insane theories mixing colour wheels and astrology.
Harook produced by Mad Robot Miniatures.