To me the red looks to be coagulated pigment. Red, silver, and black are the three colors that have this problem the most. The finely ground powdered pigment tends to glob together, creating what looks like dirt or dust in the paint. Straining is the only way to get rid of this. Before you thin/reduce the paint, warm it a little, (say baby formula warm) then strain it through a coffee filter. This will break up most of the clumps, and filter out any that won't break up. ( if the paint won't flow through the filter, you can pour in some thinner, a little at a time, to get it to go through. If the paint won't flow through a filter, chances are it won't flow well through an airbrush)
I always test shoot a scrap piece of flat styrene before I try painting the model. Since I use Evergreen Hill sheet styrene for building railroad structures, I always have some scraps of it laying around. Failing that, and knowing that there are seldom leftover parts in a kit box suitable for test spraying, I usually keep a body or two that I screwed up too much to use in the project, just for the purpose of practicing on.