Why are some apples really pink inside as well outside?

There are several apple varieties known for having pink flesh, also known as red-fleshed apples. Some examples include:

Cosmic Crisp: A cross between Enterprise and Honeycrisp, Cosmic Crisp apples have a bright pink, almost red, flesh with a sweet and slightly tart flavour.

RubyFrost: RubyFrost apples are a cross between Honeycrisp and McIntosh. They have a deep pink, near red, flesh and are known for their crisp texture and sweet, slightly tart flavour with hints of cinnamon.

Pink Lady: Also called Cripps Pink, Pink Lady apples have a light pink flesh and a sweet, slightly tangy flavour with a floral aroma.

Pink Pearl: Pink Pearl apples are small and have a deep pink, almost red, flesh. They are sweet and juicy with a slight tropical flavour.

Candy Apple: Candy Apples have bright pink flesh and are known for their intense sweetness and lack of tartness.

It's worth noting that the intensity of the pink colour in the flesh of these apples can vary depending on the climate, growing conditions, and the specific cultivar of the apple tree. Some apples may have only a slight blush of pink, while others can have a deep and vibrant pink colour.