Grey water is water from your bathroom sinks, showers, tubs, washing machines and excess water from your Domestic Grease Trap, it is not water with anything related to sewage.
In most cases it is not water that has come into contact with faeces, either from the toilet or from washing nappies. It is wastewater and considered to be a harmlessly recycled water not suitable for drinking.
The color has nothing to do with the quality of the water and it can be used for various purposes such as watering plants, flushing toilets.
Grey water is different from fresh water and requires different guidelines for it to be reused.
Here's the real definition of Grey Water - https://en.wikipedia.org/wiki/Greywater
Sources of greywater include sinks, showers, baths, washing machines or dishwashers.
As greywater contains fewer pathogens than domestic wastewater, it is generally safer to handle and easier to treat and reuse for onsite for toilet flushing and other non-potable uses.
Greywater may still have some pathogen content from laundering soiled clothing or cleaning the anal area in the shower or bath.
Treated greywater has a number of uses, some of which include toilet flushing or irrigation.