What are gray constraints in Xcode view hierarchy debug view?

You are inspecting an object such as a label that has an intrinsic content size. The intrinsic content size generates height and width constraints; that's what intrinsic content size is. The constraints in gray are showing you the constraints that the intrinsic content size generates. If you just look at them, you can see that: they say "content size"!

They are in gray because they are overridden by your explicit constraints (they have a lower priority). But they are still there, and if you were not overriding them, they would take effect (and they would not be gray).