This is driving me crazy, because I remember so much about it, but not the title or author.

It was written in the 1970s and set on Mars which has been terraformed to approximate Earth. It's told in third person present and is clearly of the "New Wave" trend of SF coming out at that period in time. Everyone is rich and has unlimited income and resources. One of the main characters is a hermaphrodite named Sisyphus. When they decide to present as female, they present as Sissy. In the course of the book Sissy seduces the teenage son of a diplomat and runs into a lot of trouble. Being born on Mars, Sisyphus has the hair of that race - black but iridescent like a peacock's tail.

I want to say the author is someone like Thomas Disch but I'm not 100% sure.