This mariachi song goes like this:
*Juan Colorado me llaman
Soy señores de Michoacán,
Y hasta los mas salidores
Al mirarme mustios se van *
Who was or is Juan Colorado?
Why do you think it was ever a real person?
There are several films about this guy, including Aquí Está Juan Colorado from the 1940s and Juan Colorado from 1966. He seems to have been a bandit from Michoacán active in northern Mexico (Sinaloa / Sonora).
From a capsule plot summary for Aqui Esta Juan Colorado:
The following is semi-speculation based on the various sites talking about the movies and mariachi song:
In the Michoacan-Oaxaca area there is a range of mountains called the San Juan Colorado (St. John the Red) range. By 1910 President Porfirio Diaz of Mexico had turned into a dictator, and was falsely accusing and jailing his opponents. Rebels led by Emiliano Zapata, Francisco “Pancho” Villa, and Pascual Orozco revolted against him, precipitating the Mexican Civil War of 1910-20. Apparently there was a man who was similarly falsely accused in Michoacan who took refuge as an outlaw (“bandito” in popular romantic parlance, but ‘bandit’ only in the sense Pancho Villa was, raiding government outposts to survive and continue the revolt, who adopted the mountains’ name as his byname: Juan Colorado. A minor player in the revolution, his legend survives as a Robin Hood type in popular mythology.
San Juan Colorado is a town and municipality in Oaxaca in south-western Mexico.
It takes its name from Saint John and from the red color of the ground. “Colorado” (literally “colored”) means “red”.