SOLVED. Sci-Fi book about a tri-gendered planet where everyone starts neuter and is 'changed' to male or female (or not) at around puberty. [s]

[Elizabeth]

The book follows a youngster who was sure he/she would be one of the ones who changes. The neuters are basically the slaves of this society. The youngster (who I always identified as female while reading the book) remained neuter but was chosen to be trained as a 'special' slave which meant basically a sex toy. Which was forbidden in the society but basically happened anyway.
This planet was an earth colony planet and the creation of the third gender had been done as part of some genetic engineering.
The youngster eventually makes it off-planet to live with people who are 'normal' I don't remember how it ends, but it was a strange book and I would like to know what it was if anyone can help.

[Sue]

This sounds like Halfway Human by Carolyn Ives Gilman.

I can't be sure, it's a long time since I read it but your description rang a bell. I thought it was strange book too, and actually a bit depressing.

[Elizabeth]

Yes this is the book. I also found it a bit depressing and odd.