Zebra Finch colours are an interesting subject. This is just a short introduction.
Zebra Finch feather colours consist of Black, Fawn, Orange, Chestnut and the absence of colour: White. All of these can be more or less diluted to produce other colours: creams and greys.
Other colours than these are not possible without hybridization. As a result, you will never se a Zebra Finch with truly Red or Green or Blue feathers.
The non-feathered areas can be red or yellow - or any shade in-between. Black is also possible, but currently only seen on young birds.
Eumelanin is a type of melanin which colours feathers grey or black. In a slightly changed form, Eumelanin is also the pigment responsible for the fawn colour.
Pheaomelanin is a different type of melanin. Phaeomelanin is responsible for the orange and chestnut colours that you find on Zebra Finches, such as the cheek patches and the base colour in the flank of the normal Zebra Finch.
Lipochrome is a fatty so-called carotenoid colour that is responsible for the red colour of the beak and the orange colour of the legs. Lipochrome is also responsible for the yellow colour of the beaks and legs of the Yellow Billed mutation. Lipochrome is never found on Zebra Finch feathers.
On other species, such as canaries, lipochrome can be found in feathers where it is responsible for the wellknown Canary-Yellow and Red colour. These colours are not possible to achieve on Zebra Finches because of the lack of lipochrome on the feathers.