A GUIDE TO GREYS
First we have pre-mixed greys that you can buy off the shelf of your local art shop. Using a selection of different pre-mixed greys at least allows you to vary the temperature and hue of your greys, rather than just relying on a mix of black and white. Pre-mixed greys can speed up your process and also let brighter colours pop against them.
Generally, I prefer mixing my own greys from a simple blend of Cobalt Blue and Burnt Sienna. This results in a dark grey that I can adapt to provide a range of interesting greys: I can lighten this mix by adding Titanium White, warm it up with more Burnt Sienna, or cool it down with more Cobalt Blue.
The blue and orange of the Cobalt and Sienna act as complementary colours – they are opposite each other on the colour wheel and when combined they form a grey mix. You can try creating all manner of interesting colourful greys by adding together any two complementary colours.