Yes I mix up colors and I use Liquitex airbrush medium to thin, luv it. It will also help to buy a bunch of 1/4-20 stainless steel nuts, use 18-8 stainless. Drop one or 2 in your paint bottle. That way after it has sat for a while, like the whole summer for me usually, It makes shaking it up real easy. Leave them in till the paint is gone and then wash off and add to the next batch. I add them to all the paints I have as soon as I open them. I also use the panty hose trick too .
http://www.liquitex.com/airbrushmedium/
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