ColorReference
Split-Complementary Color Scheme
From pg. 66 of "Color Choices: Making Color Sense Out of Color Theory" by Stephen Quiller:
"Begin by choosing three analogous colors that will convey the dominant mood of the composition. Then take the middle color of this analogous color scheme and select its complement to be used as the contrasting accent color.
"There are two ways you can mix semineutrals with the split-complementary color scheme. The easiest way is to always use the complement of the middle color ... Another way of creating semineutrals in a split-complementary color scheme is to use direct complements."
Split-Complementary Color Scheme
From pg. 66 of "Color Choices: Making Color Sense Out of Color Theory" by Stephen Quiller:
"Begin by choosing three analogous colors that will convey the dominant mood of the composition. Then take the middle color of this analogous color scheme and select its complement to be used as the contrasting accent color.
"There are two ways you can mix semineutrals with the split-complementary color scheme. The easiest way is to always use the complement of the middle color ... Another way of creating semineutrals in a split-complementary color scheme is to use direct complements."