If buying from O2 there should be no colour reservation, black is their lead colour of the 2 being offered so from that I take it will be available on both sizes. I've never used the OP3T but if this has the claimed 20% longer battery life than that model I'm sure it'll be cracking. My 6P's battery is getting worse with age so needs replacing soon by something so I'm keen to get something new.
Also keen to see how good the 16 + 20MP f/1.7 rear camera with improved focus and shutter speed is as I'm more interested in a good camera then if it has a QHD screen. Will be interesting if the partnership with DXO actually paid off.
I think I need to do a side by side with my 6P to see how I'll get on with it as want to see if I'll miss the slightly bigger screen but then I doubt 0.2" will make a massive difference TBH. I defo prefer a rear central fingerprint sensor to front though so that will take some getting used to. 6P's a killer phone, just wish Google never killed off the Nexus line as would've definitely stayed loyal to the Nexus if they didn't, perfect spec for a perfect price.