Many aviculturists and ornithologists have denigrated colour morphs as destroying the wild bird, making them unsuitable for captive-bred release programs. Whilst others are drawn to them due to the promise of rich rewards from breeding them. However, there is much to be learnt from studying mutations of feather colouration and gradually they are providing interesting insights into the function of various gene loci. Through understanding the action of colour mutations, we are learning more about the process of pigment production in feathers and about the actual genes that control the process. Aspects of feather structure contributing to visible colouration Gross anatomy is taught in undergraduate courses, but I will quickly outline it to jog the memory.
Main shaft is known as the rachis with the portion within the feather follicle known as the calamus.
Radiating from either side of the rachis are the feather barbs which in turn have projections known as barbules. The proximal barbules from one barb interlock with the distal barbules from the neighbouring barb to form the feather vane. It is the microstructure of the barbs that is responsible for the colouration of the feather. Various pigments are deposited in different layers and along with special features of barb structure, combine to produce the spectrum of colours we see in feathers. Cellular microstructure of the barb forms two main layers - a cortex and a medulla.