How can you tell the difference between male and female Betta fish?

If you have a betta fish food, and have a picture on it, it's probabily male fish. They are prettier and have longer finns. (Kinda like gold fish with long finns exept different color) The female bettas has shorter finns and are uglier, and I don't know why...
Well.. male beta fish are more colorful like red and blue.

And female beta fish are more whitish pink maybe with a few black spots

all i can say is male betas are colorful and females are more dull