A little fundamental knowledge on colour theory is essential when attempting to mix paint colours. The colour wheel, a wheel that show the basic pure hues of colours, was originally developed by Sir Isaac Newton in 1666. Artists and scientists use these wheels all the time to determine colours and how colours mix. There are many types of green from Persian green to Tea green, each are mixed slightly differently.
The Color Wheel
The basic colour wheel that shows secondary colours shows the three primary colours: red, blue and yellow. In between each colour it shows the colour that is made if you mixed two of the primary colours. Green sits between blue and yellow, as a basic green colour would need these two colours in equal measurements to make green.
Sage Green - Oils
Take a white lead paint and then tint with French ochre (this is a kind of yellow colour), lamp black and Prussian blue. As you can see this follows the idea from the colour wheel of using yellow and blue but adds a little black to slightly darken the mixture to make it the sage green colour you require. Tiniting is a careful and painstaking process of weighing a certain amount of dry white lead and then adding one grain of each of these colours and adding oil.
Sage Green - Acrylic
Use a dab of base green and think of this as one part, then add half a part (i.e. half the amount of your green) of bright or true red colour. Mix the two together, slowly adding in the red until it reaches the desired hue of sage that you require. You can tone the sage with white if you wish. You can also use a green oxide and then add titanium white until you reach the desired colour. With both of these methods you will be in control of how the hue develops. Once you find the right quantities, write down how you got there so you can achieve the same colour in the future.
Sage Green - Cheat
If you find that you are not the colour mixing expert you hoped or that mixing paints is too time consuming for you, there is another solution. Your local art and craft store or a store online will stock sage green colour paints in acrylic, poster, powder and oil. Purchasing sage green may be cheaper and easier in the long run and will save you time and effort.