The agouti signaling protein interacts with the melanocortin 1 receptor to switch between black and red pigments, creating a banding pattern in individual hairs. Mutations in the agouti signaling protein gene (ASIP) prevent this switch from occurring, resulting in hairs of uniform color.
Cats with colored 'points' have genetic mutations associated with temperature-sensitive pigment production. Pigment production is reduced in warmer areas of the body, leading to darker pigmentation in the cat's cooler extremities (paws, ears, etc.)
Birman cats have clearly defined white feet ("gloves") as part of their breed standard. This characteristic gloving is caused by a variant in the KIT gene and is inherited as an autosomal recessive trait.