John in Mortal Danger = John in Love
Let’s think about this colorful triangle of lavender, green, and yellow/sodium.
The first image is from The Empty Hearse. Sherlock’s just dropped his chips to the floor and is dashing out 221B with Mary just behind. This is right before he steals the motorcycle. The second image is from The Sign of Three. It’s John and Mary waltzing (poorly) after the photographer’s arrest and before Sherlock’s pregnancy deduction and vow to clan Watson.
The color schemes are identical and they link the scenes emotionally and semantically. If the Newlyweds waltzing put you on edge it’s not just because they don’t really know what they’re doing on the dance floor. It likely has to do with the fact that when you last saw those tints in S3, John was in mortal danger.
His heart was to be burned right out of him.
So I have nothing to add except, oooo.