The triad theme uses three colors evenly separated on the color wheel, such as all three primaries (red, blue and yellow) or here, the three secondaries (violet, orange and green). Using triads in full intensities yields a very vibrant, energetic harmony.

Another strategy is the split complementary theme: Start out with a complementary pair, such as yellow and violet.  But take one of the colors and use the colors close by on either side on the full color wheel. In this case, the yellow flowers in the foreground form a split complementary pairing with the reddish-violet and bluish-violet flowers in the background.

next: Shades and Tints