Why are grapefruits different colour?

Question

Some are red on the inside and some are yellow?

Whyy is this? is it becus some are more sour then others??

Answer 1

They are different varieties.  

Answer 2

Grapefruit began as a wild hybrid cross between orange and pummelo trees found growing in the West Indies Islands in the nineteenth century. The white was developed about 1860 as a small variety, "Marsh" with fewer seeds. The pink variants were sports or mutations that appeared in Texas grown trees. They were further developed because they were sweeter.

http://www.hort.purdue.edu/newcrop/morto...

The color is due in part to different ratios of antioxidant pigments. The carotenoid lycopene, a red pigment, is higher in pink grapefruit while phenolics are higher in white grapefruit. Phenolics are one part of the antioxidant potential of fruit juices carotenoids & anthocyanins are another but they also color the fruit. Certain classes of chemicals act to prevent oxidation in fruit so seeds have time to mature in summer heat. As the fruit ripens the starch is converted to sugar and an increasing level of the antioxidants accumulates to protect the fruit pulp so it can reach maturity at the same time as the seeds. The protection can be some combination of ascorbic acid, various phenolics, carotenoids, &/or several kinds of anthocyanins. After the seeds near maturity the acidity reduces to attract fruit eaters but  browning (oxidation) in over-ripe fruits also begins.

The reason for several variations is the same as for all genes. Genetic variation exists so the is a range of responses to the environment the tree grows in. In some locals the pink variant has the best ratio of antioxidants in another local the white version does better at protecting the fruit until the seeds mature.

Answer 3

They are just different breeds of fruit.  Its the same reason that there are different colored apples.