If you pick up a black 4Runner (or any dark color for that matter), you should start off right with a good detail. That way your paint is protected right off the get go. After doing the full (time-consuming) detail, it's just quick washes and a spray wax to keep it looking clean and protected. Here's the method I use (copied from another thread)...
(By the way, my truck is an 06 Galactic Gray... looks awesome!)
1. Wash with Meguiar's Hi-Tech Wash (in tan bottle), then rinse and leave wet. Use a chenile wash mit and start at the top of the truck, then work your way down to avoid spreading dirt on the paint. If you want to be anal, you can use the two bucket method, one for soap, the other for rinsing.
2. Clay bar the paint with Meguiar's Quik-Clay system. Use the spray bottle of Quik Detailer (included in the kit) for lubrication with the clay. Rinse or wash again after claying, then dry.
3. Use Meguiar's Deep Crystal #2 Paint Cleaner (in burgundy bottle) to clean the paint and remove the light swirls. This is a non-agressive product and is applied by hand with a foam applicator pad. It won't remove scratches, but will clean the finish and take care of the light swirls you see on a sunny day. Do small areas at a time and wipe it off before it dries with a microfiber towel.
4. Use Meguiar's show car glaze (I think it's #7 in the tan bottle). This is a pure polish and will replenish the finish with needed oils to make the paint look deep and glossy before you seal it with wax. Apply and remove by hand, same method as the paint cleaner. Make sure you use different foam applicator pads and microfiber towels for the different products.
5. Apply two light coats of Meguiar's Yellow Wax (tan bottle). Apply with applicator pad, then remove with microfiber towel.
Then you're done! Now you just maintain it for the next few months with regular washes, quik spray waxes/detailers, and/or California Car duster. This method takes quite a while, but can be done all by hand and gives great results that will last for a while. Good luck.
(BTW, I have no affiliation with Meguiar's. I just did some research on their forum when I got the new 4Runner. After trying their methods and seeing the great results firsthand, I now recommend it to anyone)