Ridin' the Trail (movie, 1940)

With the Government Remount Service unable to meet it's quota of horses, Marshal Fred Martin arrives to try and find the rustlers. Apparently just a singing cowhand dressed in white, he becomes the masked Two Gun Troubador dressed in black when he goes after the outlaws. He quickly learns Tex Walters is the leader of the gang but he must find out who is the big boss that gives Walters his orders.