Re: What makes apples have red, green or yellow skin?

Apple fruit colors of red and yellow are due to anthocyanins. The green would 
probably be chlorophyll. Anthocyanins are one of the main pigments responsible 
for flower, fruit and leaf colors other than green. Anthocyanins are in the 
cell vacuole, unlike chlorophyll and carotenoids which are in plastids. 
Anthocyanins have a wide color range depending on pH. A common science project 
is to use anthocyanins extracted from red or purple cabbage as a pH indicator.

Some flowers and fruits, such as orange, eggplant, bell pepper and tomato, and 
carrot root get their color from carotenoids. 

References


Apple Color and Taste


Carotenoids as Flavor & Fragrance Precursors 


Where does the color come from in purple cabbage?