Cat food turning red?

We feed our cat Whiskas wet food (usually poultry or meat in gravy-variety pack). 

He loves the flavours and we've never had an issue until this week. I notified a few days ago when going into the kitchen that his wet food had a red tinge to it. It's not the whole lot of it, just a bit to the side. I dump it because I think his gums are bleeding. They aren't so I think it's just some weird dye at the time.

A couple of days later, same thing. And this morning, his food was out overnight (we do this a lot...should we not?) and it's all red. I always dump it when it's red as I don't know what it is but it's never done this before.

I googled and some said it's spoilage and some said it's a red dye they put in their food now. I don't notice it on every flavour mainly the chicken or poultry ones.

Any one else has this or know what it is? We're calling the manufacturer today for find out. #creepedoutcatmom

I would guess that the change of colour is it going off. I would only feed an amount of wet food that he's going to eat all at once.  It's fine to leave kibble out so he can eat it at his leisure. 

Thanks @larrabee that's what I was thinking. Must be the heat turning it now. Luckily I'm home all day to give him a little at a time. He would eat his weight in the biscuits if I let him lol.