I feel like this may have been discussed at one point, but couldn’t find it:
Mobile UI is rendering (at least some) profile images darker than on desktop.
On the left is the same profile image rendered via Chrome’s Nexus 6 emulation mode, and on the right is the “regular” desktop rendering. (And yes, it looks just as dark on a real mobile device.)
I can’t reproduce this on meta, but why would it be happening?