Why do people say a color after what she said joke?

The phrase "a color after what she said" is a reference to the fact that some people believe that women are more likely to be sexually aroused when they are talking about certain colors. There is no scientific evidence to support this claim, but it is still a popular belief. Because of this, some people use the phrase "a color after what she said" as a way to make fun of women or to suggest that they are sexually promiscuous.