Using a color wheel divided into various shades and tints is one method of identifying possible options for color schemes. The split complementary relationship shown in this example presents many possible combinations. By varying the saturation and experimenting with shades and tints within the hue relationship, you can achieve quite a variety of palette options.
split complementary; narrow-base triangle. Straight complementary would be green red. This harmony replaces the red with the colours on either side: red-orange and red-violet. (This particular combination would not be my favourite...)