Just got a card in and upon inspection, it looks to me like a corner has been colored in with blue pen to hide whitening. It’s super hard to truly capture it in a photo, but hopefully these do a good enough job:
the first photo seems to show that one of the layers of the card is colored blue, rather than the normal white, and the hue of blue on the back corner edge looks slightly off.
Yes, probably altered. The best way to test for recoloring bleed on the edges is to stick the questionable card in a stack of non-altered cards. It’ll always stand out.