Well, my dear Bob, you have been infected. :laugh:
This is a typical (inasmuch I can tell from the picture) colony of a "staining" mold, also called a mycellium, which is probably seen only in the silver part either because the enamel was toxic to them or because you cannot see the contrast. These fungii grow in organic matter, most likely the last coat you used contained some form of cellulose or other sugar. Dusting it will only remove the paint, as it adheres to the coating (and decomposes it). Also it is possible that some rests of organic matter (even saliva may account for it) were also present in the canopy and windscreen...
My suggestion is to kill the fungii with these desinfectants and then try to scrub them off very gently with a soaked Q-tip. Otherwise, you may have to paint it over.
The name of the chemical compound is: didecyl-dimethyl-ammoniumchloride (0,05g) in Ethanol (42g).
Glad I could be of help Saúl! :dude
Cheers
Alex