Most visible swirl marks are microscratches in the clearcoat of your paint. Depending on the depth, hence severity, they can be removed to a greater or lesser degree. The other thing that helps with swirls is using a product designed with "fillers" in it. These fillers work their way into the microscratches making them less visible. Wavy or "high and low" looking areas in your paint are differences in the "orange peel".

As for the different color/different method thing... I believe 3M makes separate polishes and swirl removers for light and dark finishes. Note these are bottled in their somewhat newer consumer lineup.

Re the ML: Dot' sweat the questions! I'm glad you want to learn or at least protect the finish of your truck. 040 black (non metallic black) is perhaps the most beautiful color when clean. Unfortunately it shows virtually every little bit of dirt, sap, scratch, or chip with the same clarity. Your factory finish on your ML is clearcoat. You will not harm anything if you get wax on the bumpers. I advocate using a clean 100% cotton (seams, stitching, etc) terrycloth to remove wax on areas like bumpers. The nap is able to get down in the grain of the bumper and remove any excess wax. For trim dressing I would recommend either the old-stand-by VinylX" by Lexol or that new stuff from Meguiars that is supposed to last a long time. I believe "Endurance" is what they are calling it. You should definitely wax your ML. However since it has gone this long without any it would likely be a good idea to go over it with a polish first. Once you have either anti-swirled and polished or just polished you can then wax it. Just keep an eye for how long the wax lasts on the finish. If the ML spends allot of time outdoors then you will want to wax more often, paying special attention to horizontal surfaces. If there is anything else we can help you with feel free to ask.

Enjoy....Lee