The TJ's fender flares are not plastic.I also drive a Chevy Avalanche, that has a ton of plastic over the bed. The forum users who have tried the heat gun trick report that it fades again, usually worse. So use something like 303 on it afterwards.... sunscreen for your stuff!
That said, I've had great luck with two products.... Wipe New. Inexpensive and very easy to apply and lasts for months.
And Carworx Refinish Restorer. A bit more time consuming to apply, but also lasts for months.
For those who have no personal experience with the heat gun method that has been used successfully by so many TJ owners on their flares over the years and advise against it, give it a rest. It works better than some are guessing. If the heat gun didn't work well for me to turn my previous TJ's flares black again I sure as hell wouldn't be telling people to try it.