Ariel individually picked out all of the red books so that it was only like cool blue tones.
爱丽儿把所有的红色本子单独挑出来，只做冷蓝色调。
英语百科
Blue note
In jazz and blues, a blue note (also "worried" note) is a note that—for expressive purposes—is sung or played at a slightly different pitch than standard. Typically the alteration is between a quartertone and a semitone, but this varies among performers and genres.