Mixing Airbrush colors? Sure! Why not!! Be experimental! Here are some ideas on how to achieve some awesome colors!!
And what's a "part"? Well remember those annoying fractions from elementary school? Just think of it that way. Parts to a whole. 10 parts to 1 part could be 10 teaspoons to one teaspoon... 10 drips of the bottle to one drip. Or just eyeball and hope for the best? Maybe? But have fun! Just be sure to mix enough of your custom color to get you through your project.