OP. A photo would help. Loosely speaking though. Dirt is clinging on for dear life as there is a protective coat missing. Black wheels are notorious for this. Give them an iron out (fall out remover). Hellfrauds sell these nowadays. Do not allow it to dwell too long. My suggestion would be something like this:
1. Pre-wash solution.
2. Rinse.
3. Snow foam. Use a soft brush to work around bolts/valve etc.
4. Rinse.
5. Fall out remover.
6. Rinse.
7. Shampoo with a lambs wool mitt - two bucket method.
8. Rinse.
9. Light clay bar if need be. Nothing aggressive to scratch the wheels. Road tar is harder to see on a black wheel e.g., if you have been on a fresh road.
10. Dry. With air if you have access to an air dryer or soft towel.
11. Protect e.g., G-Tech C5 or a decent wax. Autoglym alloy spray seal works well too. You basically want to make the next clean easier. If nothing can embed too deeply then it is easier to maintain them.
12. Enjoy said shiny new wheels etc.
13. Repeat the above bar clay method and protective coat the next time e.g., if you have a decent protective coat on them then you obviously will not be applying this weekly.