Tint color transition animation slightly broken in iOS 12

[TimOliver]

When manually swiping to go back, the title text colour of the "Back" item instantly changes to the final value.

This seems to be a system level regression in iOS 12, as the similar effects in Music, TV, and the App Store are all exhibiting the same behaviour.

I tried several ways to try and "force" the transition, including manually calculating and setting an interpolated colour on each frame tick, but none of these worked particularly well.

I'm going to file a radar, and hopefully it will be fixed in a future version of iOS 12.