One of these stamps is a genuine stamp and the other(s) is a forgery. Can you tell the difference? If you are having trouble, see the "hints" and answer below.
Genuine: Black on thin colored paper. The large 2 of 2½ has a solid top with a dot in the center. Faint line under “CO” of Correos. Forgery: Magenta paper less detail, no line under “CO” of Correos. Right hand limb of “U” of UU has a hairstroke.