"Una camisa azul."
Translation:A blue shirt.
First a blue jacket..
NOW A BLUE SHIRT?!?!
WHAT IS IMPORTANT ABOUT ANY OF THAT!?!
El símbolo distintivo de los falangistas era la camisa azul curistoria.com
That article says the colour became so popular (because people wanted to be seen to be loyal to the ruling Falange party) that the party imposed a ban:
los propios falangistas...prohibieron la venta de tejido del color característico de su grupo político (ibid)
If you answered "A blue
shirts" then, yes, that would be grammatically wrong.
Additionally, "shirts" is plural, but the Spanish has "Una camisa" which is just one shirt, singular, so "shirts" is not a correct translation.