Blues was a musical genre and style of playing which the Seventh Doctor once called the "brandy of the damned". Earl Sigma often played the blues on his harmonica on Terra Alpha, despite its illegality there. Trevor Sigma, unused to this style of music, was immediately entranced by it, saying that it induced a sort of "pleasant melancholy". According to Susan Q, a "million blues songs" started with, "I woke up one morning."
After the Doctor brought Helen A's rule to an end, Earl and Susan thanked him for giving them back the blues. The Doctor then noted that there were no other colours without the blues. (TV: The Happiness Patrol)
Delta blues was a style of blues originating from the Mississippi Delta, which eventually evolved to become rock'n'roll. Ada Obiefune adored Delta blues and owned the album King of the Delta Blues by Robert Johnson, a 1930s delta blues singer. The Eleventh Doctor described Johnson as "one of the most electrifying live musical performers in the known universe." (COMIC: What He Wants...)