Sage green is an earthy grey green colour that tends to be more neutral than bright. You mix it by using sap green as the base, combined with zinc white, raw sienna and ultramarine blue. Traditionally, sap green was created by extracting a dye from buckthorn berries. The organic plant pigment wasn't permanent enough, however, so sap green is now made by mixing modern pigments that are more permanent.
Place a pea-sized amount of sap green, zinc white, raw sienna and ultramarine blue on your palette. Zinc white is clearer than titanium white, making it superior for tinting.
Put half of the zinc white in the centre of the palette with your palette knife.
Take a quarter of the sap green with your palette knife and add it to the zinc white.
Add a small amount of the raw sienna to the zinc white and the sap green. A good way to capture just a small amount is to jab the palette knife into the gob of paint on the palette and pull it straight out. The raw sienna that remains on the knife is what you add to your mixture of zinc white and sap green.
Stir the mixture well until it is a uniform colour.
Check the mixture to see whether it's the colour of sage green that you want. Paint usually varies between manufacturers and comes in slightly different shades, so you will need to adjust your mixture to get the precise colour you want.
Add more sap green, if needed, to intensify the sage green. Make it more earthy by adding raw sienna. If the sage green is too dark, add more zinc white. To give the sage green a nice cool shade, add a very small amount of the ultramarine blue. Use the "jabbing" technique described in Step 4 to add just a bit at a time. Take care doing this, as a small amount of paint can alter the colour a lot.