Task: Question Generation
Input (English): The blue and red colours of the shirt were first worn in a match against Hispania in 1900. Several competing theories have been put forth for the blue and red design of the Barcelona shirt. The son of the first president, Arthur Witty, claimed it was the idea of his father as the colours were the same as the Merchant Taylor's School team. Another explanation, according to author Toni Strubell, is that the colours are from Robespierre's First Republic. In Catalonia the common perception is that the colours were chosen by Joan Gamper and are those of his home team, FC Basel. The club's most frequently used change colours have been yellow and orange. An away kit featuring the red and yellow stripes of the flag of Catalonia has also been used.
Output (English): What are Barcelona's most often used change colors?