Grey is distinct: it’s not a primary, secondary, or tertiary colour and doesn’t have a complementary colour.
Like with black, there is a similar debate on whether or not grey is a “true colour”. For some, it could be defined as more of a bright intensity value between black and white.
Grey is nevertheless very present in numerous worlds of creation, in particular because it’s fairly neutral and is often used to produce shadows. It’s also present everywhere in today’s urban areas (it’s the hue of many materials, such as concrete, pewter, and iron). We often see it with silver, one of its derived colours.
Grey is by definition a mix of black and white, although it can be obtained by mixing blue/orange, yellow/violet red/green, and blue/yellow/orange. Depending on the proportion of the mix colours, the results will be a “coloured” grey with most of its colour coming from the larger quantity. So, there are different hues of grey, such as slate, mouse grey, taupe, grege, etc.