800 to 900 pounds are absolutely GIGANTIC black bears.

There are dozens of homes in the Smithers/Houston area (BC) which have grizzly bear rugs in them. I've seen a least a dozen of them. I would estimate those bears were likely under 500 pounds for almost all of them, with a good average of 450.

Back in 1975 or 75, there was an 875 pound black bear shot on the Queen Charlotte Islands, off the coast of BC. I saw pictures of that one on a logging beam scale. HUGE!
The Islands are now called Haida-Gwaii, because of the "Haida" Indians living there.
Brown, white and blue phase of black bears are no larger nor smaller than the black ones, as far as I know. The different colour phases are mostly main-land bears and thus smaller than the huge blacks of the Eastern States, Florida, Northern Ontario and Haida Gwaii.
I have never heard of one of the "out-sized" huge black bears being one of the 'non-black' colours.
There was one I almost shot a few years back, near here, which likely would have gone over 7' squared. That's a big black bear, normally and would weigh 350 to 400 pounds.

Most dead black bears I have seen pictures of in magazines, listed as being 400 & even up to 600 pounds appeared to be 275 to 300 pound bears.

Know anyone who weighs 350 to 400 pounds? That's a big fellow/bear. A bear carries a more limb muscle, but the "size" relationship is close.