What was Marilyn Monroe’s natural hair color?

What was Marilyn Monroe’s natural hair color?
USMC Archives, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

Marilyn Monroe was an American actress, model and singer. Famous for playing comedic "blonde bombshell" characters, she became one of the most popular sex symbols of the 1950s and early 1960s and was emblematic of the era's sexual revolution