Green granite consists of varying shades of green but has flecks of black in it as well. The black you use represents the hornblende mineral commonly found in granite. How dark a shade of green granite you want determines how much black you use. For dark-colored granite, use it as a base and apply with a natural sea sponge. Black takes over other colors if used too much. Use it sparingly as your base color, then fill it in as necessary when you add other colors.
White is an important color when painting faux green granite, no matter how light or dark your preference. The white color signifies the quartz mineral in granite. White makes the shades of green in your faux granite more visible and helps blend the colors together. Dab the white over the black base in a fully blended layer. You should not see any edges from where you dabbed with the sponge. Do not worry about using too much or too little. You can add or cover any mistakes once you have finished with your last color.
Feldspar is another component of granite and has a light green and cream color. Use a pastel shade of green to dab lightly over the white. Avoid bright and neon green shades, as they do not look natural. Apply the light green so the other colors still show through it.
Dark green helps blend the black with the lighter colors. Do not fully cover the other colors. It should only add depth to them. If the paint is too thick and covers too much of the other colors, dilute it with water in a one-part water, one-part paint mix. Wet the sponge so that it is damp and dab it into the dark green. This will help blend the color so you cannot see the edges of your dab marks.