Set 19 has maximally different hues (complements): Quinacra red and thalo green; but minimally different luminosities (both light, both medium, or both dark) and minimally different intensities (both high-intensity, both moderate-intensity, or both low- intensity). The pairs of hues oppose each other, especially when intense, but their similarity of luminosity and intensity give them all a feeling of commonality.

William Tapley
Art of Color
Color Descriptions of
Sets   Paintings