Just having a quick look at Game of Thrones [I chose Season 5 episode 5 as a random episode], and looking at the Sky Showcase version [I've a Stream box so can't watch the UHD version] which should be SDR HD.
The issue is that the picture is changing throughout from SDR HD to HLG HD. My TV plays through that [an LG] but it does keep putting the HLG banner up, and a look at the detail of the picture shows it changes, as do the exact colours.
There has been an issue [to me] in that a lot of the HD content in catch up is tagged incorrectly as HLG. For the other programmes I've watched it is consistent throughout the programme, whereas for Game of Thrones it changes sometimes within minute to minute. This will change picture mode and colour space in many TVs depending on set up and model.
It is impossible to compare directly with the version on SkyQ as they have four versions, SD, HD, UHD, and UHD HDR. The closest to Virgin's, their HD version, doesn't have this issue being consistently in SDR.
I assume others posting here are using the Sky Showcase version rather than the Sky UHD version which is only available to those who can and do subscribe to the Sky Movies and Entertainment UHD add-on or the Virgin pay per view version.