I like to use empty food coloring bottles to store and drop small quantities of thinned and custom mixed paint. I usually mix/thin in one of the small jars that came with my airbrush kit (I use my gravity fed for everything) then use an eye dropper to transfer the paint into the clean food coloring bottles. Slide a finger nail under the the dropper top and pull it out for cleaning or to add paint.
You can then just shake the bottle and drop and add only as much as you need to your airbrush cup. Put the lid back on and its good till the next time that you need it.
Please feel free to share your method or containers.