Most of the Testors enamels intended for plastic display models are NOT fuel proof. The metalic enamels are not even resistant to short exposure to low nitro content fuel. Aluminum color is the worst, comes off faster than it went on.

The new Acrylic paints for plastic models are fuel resistant, sufficiently for use in areas away from where you commonly spill fuel. Some of the colors may darken a bit with short exposure to exhaust residue.

You can add a clear coat of something such as Lusterkote over some of the above paints, and then you have a fuelproof finish. Test for compatibility... I've only tried a few colors so far.

Try Rustoleum....comes in many colors can be bought at the hardware...
The finish will blush if you spill fuel directly on it if you don't wipe it off in a short time...but other than that it's great...