Brown eye color dominates over blue, dark hair over light. How do you define this?

In genetics, a conventionally dominant trait is denoted by some capital letter, and its alternative, that is, the opposite to a given trait, is denoted by a letter of the same name, but small. If several traits are listed in the genotype, then each trait has the designation of letters with different names.

Brown eye color is dominant over blue. Then the brown color is designated through the letter “A”, and blue – “a”. Dark hair is dominant over light hair. Then dark hair color will be “B”, and light hair color will be “b”.