You're right on it Pascal: the AMI seems to be the only one with black date and day rings, and photos in catalogues always show white discs with black fonts.
Still there is a fabolous 510.500 with black rings on the OtD gallery, cf.

http://www.onthedash.com/Guide/_Chronographs/86.1000_Series/Reference_510.500/Reference_510.500/

and I must admit I find it suits wonderfully, so much so that I have asked Abel to put them on my 510.500 he's restoring if the dial is not too discoloured to contrast!

On the other hand, having seen quite a number of non-Heuer L5100-powered watches myself, black discs were the norm for the wonderful Fortis Cosmonauts in its later L5100 incarnations (and also for the current Val.7750-based model).

Cheers.
Fabrizio

Fabrizio