The key to the big chests in temple of lies blends in with the color scheme of the floor tiles and makes it very difficult to see.
Yeah, this key and the mini-boss portals in The Barrens are both just things I tend to run into and say “Oh, I found it!” or see when checking the map and have to go carefully investigate, haha.
I actually have red green differentia myself. I have more trouble finding the key in Friden’s realm though, since it’s half buried. I think a lot of these things could use the Icon animations that was added to Azural’s favor gems recently.
The X marks the spot is really difficult to find in some tilesets too, but I don’t complain about that because I feel like it’s part of the flavor to have to use the in-game map to find where the X spawned.