Has anyone done this, what were your results? I saw herculiner came in grey, which would match my interior, but I was wondering how fast it gets dirty and any other drawbacks when compared to black.

It will be good to put under the carpet, but the noise and heat is more than I was willing to take without the carpet. You and your passengers will have to wear shoes as the floorboards will get hotter than bare feet can stand, especially on extended trips.

Only experience with black is on Jeep floorboards and the bed of my truck is color matched forest green. I can tell you the lighter colors look good when new, but you can see all dirt marks after a couple days, even when you clean it. Here is my truck bed.