"Una camisa azul."

Yes camisa for shirt and camiseta for t shirt ...i think

No dear I dont think

Only because in english we dont say "the cloth", "las ropas" isn't used.

Ropa stands for clothes

Historical note:

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.