Updated: Jan 12, 2021
Grey is considered a dark colour when doing laundry. As you know, your washing should be split into colour groups. Your white should have a pile, your lighter colours should and so too should your darks.
That being said, it also depends on it's shade. Many greys are closer to white in the shade and few are closer to the dark side.
However in general your grey clothes should go in the dark pile.