Red hair color is the fastest fading color. It fades in the sun, it fades when rinsed, it fades when washed with color safe shampoo. The hair is constantly seeping red dye when it comes into contact with a liquid or cream.
And these mutations aren’t dominant alleles, because they arise from reduced pigment production, reduced function in pigment receptors, or other interference with the pathways that turn most people’s red hair color dark. This means that getting an allele with the “normal” function will reduce or remove the effects of the allele that causes blonde or red hair.
Blondness in these groups is due to a novel mutation that occurred in the population that initially colonized the islands. The mutation is a single amino acid change in the protein . It is likely that the mutation destabilizes the protein, causing it to unfold and remove the pigment that the gene normally produces, causing blondness. This red hair color inferred through the presence of an analogous mutation in mice in the same gene that causes light brown fur instead of brown fur. The mutation is recessive, meaning that both copies of the gene need to be mutated in order for the person to be blonde.
The main reason for that would have to be related to the environment that the ancestors of the red hair color. In a climate where there is more sunlight and warm weather dark hair became an adaptation for that certain environment. Dark hair offered protection from the warm weather because of its higher melanin content which was able to serve as a block to sunlight.