Hey Jonathan,
The closest to a recognised sub species is Testudo Hermanii Peloponnesica an isolated population in Greece. They are very dark in colouration. I have a male that is almost completely black.
If I remember rightly either the Romanian or Bulgarian populations are considerably larger than other THB but not to the extent they'd be considered a sub species.
Danny's guide to the Horsfield sub species is here:
http://shelledwarriors.co.uk/forum/s...ad.php?t=28051