I've heard that Wheel Brite clear lacquer will fuel-proof Rustoleum silver.

I recently discovered this fact for myself, followed shortly by the discovery that brushing dope on sort of works -- the dope does, indeed, fuel proof the Rustoleum.  But the Rustoleum isn't fuel proof, so brushing on the dope gives it a "brushed on metallic paint" effect, which you hardly want.

For some reason, the next canopy I painted was sky blue...

Use any silver paint you want then spray a coat of Klass Kote Epoxy clear.  Definitely do a test panel first.  Contact Nate at Klass Kote for the low-down on a modified spraying technique to help the Klass Kote "mate with" the color coat rather than attacking it if they are less than totally compatible (are any two chemical compounds ever fully compatible?).  It goes something like this: spray a mist coat from a couple inches farther away then you normally spray, dry a while, repeat the mist coat, dry a while, spray a full normal coat.  Now your subject is fuel proof and practically bomb-proof.  Klass Kote is TOUGH.

Enjoy!