Vinegar should help, here we sometimes use a splash of lemon for our chef whites in a hot pot of water.

Grey whites are a sure sign of mixing detergent with bleach in the laundry.

I’d suggest any whites gone grey are a loss. There is a great laundry product for whites called bluo here in Australia that I recommend and use for my chef whites.

https://033.drakes.com.au/lines/bluo-liquid-blue-laundry-brightener-250ml