I have a few built models for which I would like to 'define' and delineate the space between rudders, ailerons and elevators control surfaces. Rather than a continuous paint pattern. Any ideas? Thanks.

if you are looking to make panel lines stand out, then shoot them flat black and then re shoot the planes original color making sure to stay off and out of the lines.

is this the look you were going for?

You could use a pin wash to create "shadows" in the hinge area. Another idea is to very slightly change the colour of the control surfaces. Many WW II aircraft had fabric covered control surfaces, which is often quite evident from its different sheen even when they're painted with exactly the same paint as the adjacent airframe.