The study originated in “What Sells Art?,” a 2013 op-ed by Philip Hook, then a director and senior paintings specialist at Sotheby’s who asserted that “blue and red tend to be good news ...

But blue pigment is rare. Instead, the blue sported by bluebirds comes from tiny air pockets inside the feathers, which scatter light to create blue. Red feathers, however, rely on pigment alone.