I remember that whenever the Borg vs Nadal claygoat argument used to come up lots of Nadal fans would argue that Nadal is clearly better because Borg wasn't able to win the US Open on green clay. Apparently, if it was played on green clay nowadays Nadal would dominate there just as much as he does at Roland Garros. I can't be bothered to dig up quotes but I distinctly remember phrases like "Nadal is the best on any type of clay".
Well... suffice to say, I think blue clay has debunked that argument.
Nadal/Borg are red clay goats.
Yes, they always bring up Borg's losses on har-tru to dilute his complete dominance at his peak. He only lost 3 matches on red clay in his prime years from 1977-1981. One of them being a retirement when up 4-1 in the first and none at RG.