Well this thread looks like it went off topic some time ago...
I picked up a 2021 GT a couple of weeks ago. Colors were identical, but the dealer said that Triumph actually raised the price of the grey model by a little bit. Didn't bother me as I preferred black anyway. Dealer told me nothing had changed between the model years though (can't swear to it as I don't have a '20 also). They had two '20s on the floor (one GT and one R), and two '21's that had just arrived and were still in crates (again one R and one GT). They were offering $500 off the '20s without asking. I ended up getting the '21 GT for $1000 off.