If you are staying strictly with gas, Krylon colors will work without the benefit of clear coating.
What can happen with uncoated color is a slight leaching of the color pigment from the surface if raw gas is left for more than a few seconds. That really is not a problem 99.9% of the time though.
Also, don't use straight denatured alcohol as a cleaner to remove oil residue because it will attack the surface of the paint in a hurry.