The dark water is carbon dust from the new filter. It's normal.
Flush the system. Turn on the cold water faucet and run water for 5 minutes. The water should run clear after that.
If the water stays dark after flushing for 5 minutes, check the installation. Make sure you connected the filter correctly. The existing cold water line goes to the outlet port on the top cap. The included braided hose connects the shutoff valve to the inlet port on the bottom cap.
Air bubbles can also cause cloudy water for the first 1-2 days. Let a glass of water sit; the bubbles will dissipate.