I did not notice any "yellowing" but did notice that he was flustered. He had the same look like he had in the playoff game vs. the texans and earlier in his career (GB, Patriots etc).
This was probably due to a variety of reasons; porous OL play, no WR separation, lack of running game, poor coaching and I'm sure he also felt the pressure to keep up with Mahomes. He was pressing.
I'm not worried about Allen, he will learn from this. After watching Allen for 3 years now, my eyes tell me that the moment is not too big for him.