Question

Why are carrots orange?

Answer 1

They can be any color, but nowadays, we associate carrots with the color:
orange.

They can be white, purple, and a lot more colors.

Farmers used to plant different colors, but...

Quote an article why farmers now mainly plant orange carrots:

"In the 17th century, a strain of carrot was developed that contained higher amounts of beta carotene -- the first orange carrot. Dutch carrot farmers started growing the new orange carrots in honor of William of Orange, and the traditional, more colorful carrots, were tossed aside for these newly fashionable orange carrots."

The discovery of new lands with settlers bringing their traditions spread the farming of orange carrots instead, across the world.

And happily ever after, we now associate carrots with: 
Orange!

Answer 2

 This is because two genes are responsible for the accumulation of pigments in the roots of carrots. Well, there are several other different pigments as you can see: white, purple, and yellow.
However, nowadays, orange carrot is mostly available.