Doing a foggy background in acrylic?

[adammelo]

How do you go about doing a foggy background in acrylic for example say theres a valley, and in the background you'd like to show your depth by making it foggy and cloudy, how is this done?

My assumption is just gray paint, but being as im a novice it sounds wrong to me...

[Viridis]

Depending on your reference, you actually want a lot of blues and blue-greys; as well as mixtures of neutral greys. Atmospheric perspective means that things get fuzzier and bluer in the distance, so you probably want lots of light blue, white, neutrals, and a little bit of grey.