^ You don't have a cover anymore, the dress-up doesn't count.
While I agree if you have a Supercharger you should clean up the bay and show it off, but not everyone feels this way.
I have seen stock ones painted just a little bit, fully repainted with flames, some even modded to vent off some heat and then painted. Truthfully most of the good ones are old builds and the members are long gone, you will have to use the search bar or google and find some. Basically same for a how-to as it is painting anything else that is plastic, sand, primer, paint, clear. Prep work is the main thing, and using good high temp paint is the next. If you don't have the skills to paint, just leave the cover off and look into other options for making the engine bay pretty.