You may need to be patient/lucky/willing to travel as only 593 Auto Coupes seem to have made their way to the UK, so ruling out black reduces your options even more.
I'm with you on not wanting black though..
Told myself twice after owning black cars, never again.
(Although they do look stunning when clean and glossy)
I was convinced I didn't want black, but somehow talked myself into Ruby Black for my first Z4 - I think the Pearl Grey leather helped!
Anyway after a bit more digging on here https://tonyz4c.z28.web.core.windows.net/index30si.html
it seems 221 of the 593 Auto Coupes were black so you are fishing in a pretty small pool, especially when you want low mileage seeing as the newest ones were built 17 years ago.