That’s a very nice example. The tank appears to be the correct color to me. I don’t think they ever were a bright white. They may have been new, but I’d hope someone old enough to have handled a new factory saw would chime in.
The filler caps look correct also. The knurled ends worked surprisingly well. Also, there should be a chain attached to the center of the caps on the inside and a spring retainer at the end to keep it from falling when you fuel.
Not much more $$$ than a new 881. It’s a bit too nice to run though, that’s a museum piece.