(covers information from several alternate timelines)
Blues was a type of music.
In 2259 of the alternate reality, having received word that he was going to be sent back to Starfleet Academy following an incident involving the violation of the Prime Directive on Nibiru, James T. Kirk visited a bar in San Francisco where blues music was played over the speakers. (Star Trek Into Darkness)
In 2368, Commander William Riker asked Amarie if she would play some blues music on her piano. She claimed to know seven shades of blues, then asked him if Andorian blues was a good choice, and began playing it for him. (TNG: "Unification II")
In 2399, Cristóbal Rios was listening to blues and drinking alcohol when his ENH interrupted, telling him how excited he should be that Jean-Luc Picard would soon be on his ship. Rios, annoyed, deactivated him. (PIC: "The End is the Beginning")