Many of the heat resistant paints turn a dark grey shade after a while. A tip I was given was to use black lead ( the stuff for polishing victorian cast iron fireplaces!) buffed up over the paint. Worked a treat
Hammerite barbeque paint.
use the aerosol version.
Used it on my old translp and as long as you have prepared the surface it is fine. It has a matt finish though if that is an issue.