Yellow Peril !!???

if it's beading up with several brands,i'd have to say sand it smooth again,then clean it with alsohol,prime it with a white primer.sand that,alcohol again,then it should be fine

also,another thing to look at if your airbrushing,could be the possibility of some type of contaminant getting into the paint from there,if oil based,,is there excessive moister in the line?

No, it's not the fact that the paint is yellow. The surface is acting as if it is hydrophobic. Are the areas you are trying to paint gloss or flat? If gloss, what kind of paint did  you use under the yellow?

What did you use to clean and degrease the masked areas?

I cleaned the whole kit with alchohol prior to primer, primer is Halfords grey plastic primer, I then cleaned with alchol before applying the yellow. The rest of the kit is painted and I had no problems with any other colours.  I have a moisture trap on my AB line.

The fact that you tried several different brands of paint with the same result indicates that it is something odd about the surface, or there is a contaminant in the air brush. What was last in the airbrush, and what did you last use to clean the airbrush?

Too much needle lubricant in the airbrush will produce the same kind of result.

I'm not familiar with Halfords plastic primer. Is it an enamel or an acrylic?

If the original yellow (the one that first did not work) contaminated the surface further, that would confuse the problem.

The most obvious solution is to wet sand the surface with 1000 grit, clean, and repaint, (as mentioned by Lone) but I'm trying to figure out how to prevent the problem in the future.

What alcohol did you use? Some rubbing alcohols contain additives/contaminants not compatible with paint.

I will rub down and reapply tomorrow, as far as paints,alcohol etc the only thing different was the first yellow I tried, it was Citadel Paint and I thinned it with water. It may well have been this paint as Ihave never used it before, I only bought it because the Yellow just looked the perfect shade for the cowl, oh well you live and learn. I shall update tomorrow evening.