I am working on an F-16 and there are supposed to be black panels that are in the middle of a light gray background. So I dutifully painted the background light gray and tried to pick out the panels with a finepoint sharpie… but that didn’t work. I’m afraid to try this with a paintbrush, because my hand shakes really bad when Im doing ticklish stuff like this.
The link below is for PE detaisl but may be able to be adapted to plastic kit parts.
An alternative wuld be to try painting it black first, then taking some gray paintthat has been thinned down, not as thin as a wash, but will flow easily. Load a pointy brush with the gray and “flow” the gray around and upto the edges of the panels.
I’ve had good luck with that technique. You can also use the same method to apply a mask by thinning a liquid masking agent and flowing that around the panels. Several applications are necessary. If you do this, you have to remove the mask as soon as possible—or it will stay there!
You paint your overall base color in enamel and let cure. Take acrylic paint and paint your detail. If any detail color spills over to the base color, take a paint brush with a good edge, moisten with water and clean up the edge around the detail. Sometimes my had shakes a lot and this method has gotten me some pretty good results. I got this idea sometime ago on another forum.