Paint mixing and airbrushing error

While I'm hardly the expert, you should be able to mix different colors of the same brand. People do this with Tamiya all the time, mainly because their color selection isn't as comprehensive as other brands. For instance, I've seen a number of variations for mixing Tamiya colors to get "accurate" shades of some of the RLM colors, combining as many as 3 different colors. Ideally you would be able to get the right color out of the bottle, but with Tamiya this isn't always possible.

It's entirely possible that some of their colors don't mix well...I know that some hand brush better than others, and some are more difficult to AB (like their flat aluminum...gave me trouble anyway). Personally I prefer the right color out of the bottle rather than having to mix.

EBergerud

The post in question suggested that paint mixing can lead to pigments that don't like each other coming out of the same airbrush and causing trouble. The gent argued the merits of using dedicated colors.

I think this person was talking out his rear orifice. Within a particular brand's range, there shouldn't be any issues. The actual pigments only make up a very small proportion of any given paint and are often inert or have been chemically stabilised. The rest of the paint is made up of binders, fillers and reducer (collectively known as a carrier). .

Having said that, it is possible to have problems occur when you mix paints of different brands where their carriers are incompatible.

For example, many people assume that the term "acrylic" simply means water based. While at one level, it's true, (many, but not all acrylics are considered water soluble) it does not mean that they can all be mixed. For example. Tamiya and Gunze Aqueous acrylics (and Testors MM Acrylics) are alcohol based, Vallejo acrylics are "water" based and Gunze Mr Color are described as "solvent based acrylics" and are not water soluble. While you can cross-mix between Tamiya and Gunze aqueous acrylics, you can't cross mix between, say, Tamiya and Vallejo acrylics, because their basic formulations are incompatible, even though both types are acrylic.

Generally, you will encounter fewer problems mixing enamel type paints as they are, mostly, similar in formulation. 

I have long mixed paints from a single line. I have even mixed enamels of different brands.  While there may well be a possibility of a problem, in my experience it is very rare.

I find that often I want a color for which there IS no dedicated color.  An example- cast aluminum. I always mix storebought aluminum with a medium flat gray to better represent aluminum castings. I find many steel colors to be too bright for an aged steel surface.  Sometimes I want to weather a color and mix white or light grey with it.

Every time I have had airbrush painting problems, I have traced it do something about the airbrush (leaking teflon gasket with Badger, or not cleaning it well enough after use). I've been modeling for sixty years, using an airbrush for forty. I don't hesitate to mix colors when none of my available colors give me the shade I want. I do ordinarily, though, stay with same brand and type.  I also do use paint brand's own thinner for actual paint thinning, use hardware store thinner only for cleanup.