I’ve not been able to find a pre-mixed paint that is the right shade/tone for using as backgrounds. I always find them to be too dark so always end up having to mix them in with some white. This means that I have to make sure that I mix the right amount so I’ve enough to fully cover the background at least twice plus factor in for any “accidents” that may need sorting out. But at the same time I don’t want to end up with too much that ends up drying before I get to use it on another picture and goes to waste. Sometimes I get it right and sometimes I don’t, at least I ended up with too much this time. There’s nothing more annoying than not quite having enough but not being able to mix the exact same one again so you just end up having to repaint it all with the new stuff because doing that is quicker than spending ages trying to mix a small amount of what you had before.