This uses two pairs of complementary colors that are not evenly spaced. For example, a palette of Yellow, Violet, Blue, and Orange. The "shorter" sides of the rectangle mean the colors are closer together, offering a slightly more harmonious (but still high-contrast) look.
The beauty of the tetradic scheme lies in its inherent tension. Because you have two sets of complementary colors, you get maximum contrast and maximum variety. It allows for a richness that simpler schemes can’t achieve. It feels complete; like you’ve used the whole crayon box. what is tetradic color scheme