Invisalign causing severe yellowing. Anyone seen something similar before? (Photo)

I had evenly white teeth before starting Invisalign treatment. By my tenth aligner, my teeth were severely discolored near the gum line, weirdly every tooth was exactly half yellow (from the gum to a line in the middle of the tooth.) The tooth discoloration is getting only worse, even though I brush regularly, use mouthwash, floss after each meal, and drink lots of water. The discoloration happened uncommonly rapidly. Anyone seen something similar before?