Question: How does a body (human or animal) produce multicoloured hairs?

Jason Chu answered on 22 Jun 2018:

So we are able to express different hair colours based on our genes.
So my hair colour is very dark brown/black. So my genes express a variety of dark pigments to produce my hair colour – in humans this is melanin.
However, birds (often very colourful) – don’t just have melanin. They also express a range of carotenoids, and porphyrins. A combination of these three if vary proportions leading to ranges of colours from bright reds, to olive greens.

Essentially, our DNA have genes which enable us to produce different pigments (diff proteins/molecules) which come in different shades of colours. So imagine a biological palette of paints that our body can produce.