Locate the position of your yellow on a color wheel. The color wheel should have as detailed a range of intensities and hues as possible.The more intense yellow is nearer the center of the wheel. Add this yellow to your color to increase its intensity.
Locate the purple on the opposite side of the wheel that is the exact complement to your yellow. Add a small amount of this purple to your yellow to dull its intensity. Add white to dilute the intensity of the yellow.
Change the yellow's apparent intensity. Place the yellow next to darker, less intense purples to make the yellow seem brighter and more intense. Conversely, the yellow will seem less intense when set next to brighter, concentrated oranges and greens that surround yellow on the color wheel.