The jersey of the leader of the general classification wans’t always red. Actually, this is a very new invention at the Vuelta a Espana.
Colors of the leader jersey at the Vuelta a Espana
1935-36, 1942, 1977 orange
1941 white
1946-50 white with a red stripe
1955-1988 yellow
1989-2009 gold
2010- red