I provide a complete list of all the normal colours I use in my Online Art School. I normally use these same colours for every subject I paint and rarely ever add a “special” colour. When I need different colours, such as varying the shade of greens for a tree canopy or grass, I add different colours to the mix until I have the different shades. I use darker transparent colours for the shadow area, more saturated or less saturated (meaning grayed or purer colour) as the second and third layers, and lighten the greens with yellow to keep the saturation (purer colour) first, and only add white at the very last stage when, perhaps, I need better covering power. It is an advantage to have 3-6 different colours to help achieve the 3D effect of trees or grasses. In my Online Art School tutorials, I give detailed instructions on how I mix my colours and also name them as I proceed and give reasons for the additions. If you need a very basic list of colours to use I would suggest Titanium White, Ivory Black, Sap Green, Burnt Umber, Windsor Lemon, Cadmium Yellow Light, Cerulean Blue, and Alazarin Crimson.