Why do K5 IIs reds look different?

I did some informal tests at home. I dimmed the light way down low so that I could barely see anything in the viewfinder. I used the DA15 and the FA31 to take pictures of my son and wife. The K5 blew it all the time. The K5IIs was mostly on target. The AF speed is also better on the K5IIs. It is more decisive, while the K5 grumbles and mumbles before locking.

The number of samples are too less to make any definitive conclusions, but it seems like the K5IIs definitely does better in low light.

The DA15 scene (@F/4):

K5IIs crops:

K5 crops:

The FA31 scene (@f/2.8):

K5IIs crops:

K5 crops: