Tinted ground filler?

[Lowtardog]

Emulsion paint + sand + PVA. Sets rock hard. Make it thick or thin as you like. Any colour you like. Overlay over any base material you like - foam, wall filler, whatever. It sticks like a leech. Easy to work while wet. Costs peanuts.
Why doesn't everyone use it? 

Similar technique here though I use a big bucket of a reptex type wall paint and add sand to taste, I sometimes pre colour it but not often

[Darkoath]

What exactly is emulsion paint?  I have never heard of it.

[Gluteus Maximus]

What exactly is emulsion paint?  I have never heard of it.

A water-based paint where the paint is "emulsified" into the water. Used mainly for painting walls etc and usually comes in matt or semi-gloss variants. Some DIY stores here in the UK will mix up customers' own colour specifications, so for example you can match GW's Goblin Green should you wish. I'm sure you have the same thing in the USA, but under a different name.

It's like "spackle". We have similar stuff here, but not under that name