I read this novel between 2001-2004 so published sometime before then. I seem to remember that it was by a female author but I’m not certain of that.
A female protagonist who can see in ultraviolet volunteers to be injected with single-cell organisms which she must mentally communicate with and control. They have very short lifespans. A male character was also injected but lost control and they took over his mind.
The organisms come from another planet and there is a minor character who was a genetically modified human-gorilla hybrid.
Edit: The female character rebuilt her body by the organisms choosing to be very strong, a 10/10 for muscles. The male character mentioned above was an artist and painted or created something in ultraviolet knowing the female could see it. Houses are “aware” but not sentient. Much of the story takes place in a city, and I remember a type of public transport similar to elevated monorails. During one part, there is a party with elaborate dress described.
Edit: This is an Elysium Novel. The girl is an artist and she agrees to let "brain enhancers" in her skull - microscopic creatures living in the outer linings which communicate by flashing lights.