Question: why are you blonde? tell me a biological reason why people's hair is different

Claire Shooter answered on 18 Jun 2014:

I’m actually blonde because I pour bleach on my hair! It’s brownish underneath…
We don’t have the finer points of hair colour genetics completely understood yet: There are so many different shades possible that it is likely that several genes control the finer aspects of hair colour. In a broad sense though, it works in the following way:

Your hair colour is made by two types of pigment: pheomelanin and eumelanin. Pheomelanin can make hair blonde or orange (depending on which type you have) and eumelanin makes it black or brown. Let’s label these as follows:
-Pb (pheomelanin blonde)
-Po (pheomelanin orange)
-Ebr (eumelanin brown)
-Ebl (eumelanin black)

Everyone has two copies of the gene which can be any combination of these. This combination is known as your ‘genotype’. The hair colour you get depends on which combination you have – darker colours are stronger and will influence the hair colour more. The colour you see from the genes you have is called your ‘phenotype’. Po is recessive and will only be seen phenotypically if you don’t have any copies of the stronger pigment genes.
Broadly, the combinations are as follows:
Pb/Pb or Pb/Po= Blonde
Po/Po = Orange
Pb/Ebr, Po/Ebr, Ebr/Ebr = Brown
Ebl/Ebr, Ebl/Pb, Ebl/Po, = Dark brown
Ebl/Ebl = Black

Your parents each have two genes so there are four you can potentially inherit: This is why two people with brown hair can have a ginger child. If both parents are Ebr/Po they will have brown hair, but their child has a 25% chance of getting both Po genes and a ginger phenotype.