If apples are red, why isn't watermelon green?

The color of fruit is probably not something most native speakers of American English spend much time thinking about. And they don't need to; it's something they just know.

If the fruit is the same color on the inside and the outside, then it's a no-brainer. For example:

Oranges are orange.
Grapes are green or red.

But when the color of the skin or peel is different from the fruit itself, it gets confusing and can seem pretty random. Usually, the rule of thumb is that the fruit is whatever color the skin or peel is. For example:

An apple is red.
A banana is yellow.
A pear is green.
A strawberry is red.

On the other hand, some fruit is described by the color it is on the inside. For example:

Watermelon is red.
Kiwi is green.

It turns out that the color a fruit is described as being has to do with how native speakers usually encounter it or picture it in their minds. Do they see it as a piece of whole fruit, so it is the color on the outside? Or do they think of it as cut up, so it is the color on the inside?

Example:
-If apples are red, why isn't watermelon green?
-Good question! I have no idea!


True story:
I have used lots of idioms in this entry that haven't been defined yet, such as 'no brainer,' 'pretty,' 'random,' 'rule of thumb,' 'on the other hand, 'it turns out that,' and 'Good question!' I will define them in the future and then go back and link them with their definitions.