If using three adjacent colors, try using the middle one as the predominant color, and the others on either side of it to a lesser extent. Here, blossoms on the bluish side and reddish side of violet are subordinate to the violet blossoms.
When using analogous colors, try keeping their intensities the same. Intensity refers to the amount of gray an instance of a color contains. An intense or saturated color has little or no gray. Desaturated colors (called tones) have more gray added, and appear muted.