Manchester United's nickname?

Manchester United's nickname is the Red Devils right? So why do so many websites keep referring to them as the Reds? Even the official Manchester United website www.manutd.com refers to them as the Reds. Why?
Update: @Eddie and MR ANFIELD ACES I know Manchester United is the Red Devils and Liverpool is the Reds. You guys just basically repeated what I said in my question.
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