6000 gallon AG pool with a cartridge filter and salt water chlorinator The water turned green and added a bag of shock the water is now milkycloudy How can the water color be fixed?

Although one bag of shock does treat usually 10,00 gallons, that is assuming a clear pool to start with. Since you had an algae infestation, more shock will be required. A simple rule of thumb is when treating problem water to double or even triple shock the pool. Simply put, there wasn't enough shock there to finish the job. Test your water for chorine. Most shocks are chlorine based. If your chlorine is low or zero, it will confirm the need for more shock.