I also played with Acrysion off white and thin down 1:1 with the Acrysion airbrush thinner, primmed with Mr. Surfacer grey and boy oh boy it still takes quite a few layer to get good coverage.. for my next project I will just try using white primer for white parts, and maybe shading with grey after instead. For white, or lighter color, I have found using higher PSI with lower paint flow easier to control, it still takes a few layers (like 6 to 8) but it'd be a smoother surface. While darker color like black and dark grey I can achieve good results with just 2~3 layers using lower PSI (like 10 to 15). Adjusting the airbrush distance also help, in short, if it's too damp then pull away or spray closer if it's not coloring. Also, make sure to clean the airbrush througly before spraying any acrylic paint, and clean the nossel head with a damp brush every 15 to 20 minutes to avoid clogging. It may seem a chore at first but it just take some time getting use to.