I was keen to see which race they were and was surprised to see males that suggested both rosacea and griseiventris present. One male was uniformly dark grey below sharply contrasting with the bright pinkish ear coverts patch; very attractive actually. Not to mention exciting, I've never knowingly seen griseiventris outside Hokkaido. According to Brazil (East Asia Fieldguide) rosacea is the common winter race in Korea and griseiventris the common race in Japan, but all I've ever seen in Kansai are rosacea. However, when the birds moved on I checked the images (which was in itself a huge disappointment, but more of that in a minute) and saw there was a slight reddish tint to the grey in the centre of the breast, this was even clearer when viewed later on the pc. As far as I'm aware griseiventris is completely grey below whereas rosacea is variable. Therefore I presume this bird must be towards the 'grey end' of rosacea, it's certainly the greyest I've seen, and I can well imagine how easy it might be to misidentify as a griseiventris on a brief or distant view. Though for all I know they may come even greyer than this.
I was slightly surprised that almost all the females showed conspicuous white in the outertail feathers whereas the only two males I saw well enough did not. This seems to be variable in some (all?) taxa so it's probably no more than coincidence.
Coming back to the other big disappointment, looking at the images I realised the setting dial had moved onto TV and there simply hadn't been enough light to support the shutter speed the setting demanded. So all the shots I got, or the vast majority anyway, were seriously under-exposed and I've had to lighten these images to be able to use them.
A nice side by side: the upper bird was an obvious rosacea (as later shots will show) even though it doesn't look very red-breasted here. The grieiventris-like bird below has very uniform grey belly and flanks abruptly abutting the white vent and lower belly, this was apparent from all angles.
Below is a series of three shots of the same duo at different angles. The rosacea can look very pale below or less so, redder or greyer, depending on the angle. The griseiventris lookalike is very consistent in appearance.
Three shots of the same two males together, one clearly a rosacea while the other had me believing I had a great comparison of both races.
Below is the same rosacea looking even redder in this image. Following that are two shots of the griseiventris, the last showing a distinct reddish hue.
Two shots of the griseiventris-type, the latter heavily cropped and lightened revealing a distinct reddish tint to the centre of the breast.
I was also interested in getting some shots of females and when I returned to the males there was only one, which may or may not have been the original rosacea.
If males can be tricky then what hope is there for females?
The females are a quite beautiful combination of soft, subtle colours and identification issues aside I'd have to say I prefer them to the males. The following bird perched higher catching more light so my shutter speed disaster didn't reek quiet so much havoc.