Mix equal amounts of black and yellow paint. If you plan to create a large batch, create a small test batch first to determine proportions. Add more yellow to the mix if you want the color to appear more yellow. Adding black will darken the tone.
Mix a medium-tone green with purple or violet. Look for a green color that rests at the center of the spectrum. Add to it the violet tone and adjust the ratio until you achieve the shade you want. You can also add yellow or orange to medium green to achieve an olive with a warm undertone.
Mix earth tones, such as ochre or sienna with blue or blue-green paint. Start with the earth tone and add the blue paint color until the olive you desire materializes. Mixing paint colors takes patience and care, but achieving just the right hue is well worth the trouble.