Miller reports that a "theory of the orange gene" is somehow connected to personality traits. She points out that the Cheshire Cat in the children's classic Alice In Wonderland was a red tabby. And we know how nuts he was!
The orange gene is sex-linked (X) and not on the same chromosome as all the other color genes. Therefore it is possibly only for female cats, because they have two X genes, to have black and orange coat colors at the same time. Males with their XY chromosomes, can be black or orange, but not both. This means that calico and tortoiseshell cats are always female - and female cats are often not as mellow as males anyway.
*This information was gathered from "The Cat Behavior Answer Book" By Arden Moore