Milky/white coloured water indicates a bacterial bloom, bacterial blooms are more common in young tank set ups, but can come about when a large change in water quality happens. Doing regular once weekly 30-60% water changes with dechlorinater and substrate cleaning sessions will help stablilize the water quality, if the bacterial bloom is really cloudy, then you should increase the airation in the tank and do once daily 20% water changes with dechlorinator.
Green water indicates an algae bloom, keeping the tank lights turned off for longer and doing more regular water changes and substrate cleaning sessions will help reduce the nitrate and nutrient levels in the tank which are fulling the algae bloom.
Brown/yellow water is usually a side effect of having new bogwood/mopani wood in the tank which releases tannins which stain the water a sort of tea colour, or is a result of simply not cleaning the tank properly or often enough.