How do you change the colour of a Gui?

Hi, first off Happy easter. I always come across this problem when ever I am doing something with GUI's and decided to ask you guys about it. When I am trying to change the colour of a GUI (like a frame or textbox), I get this error message

(Color3 expected, got number)

I tried using

Frame.BackgroundColor3 = Color3.new(255,255,255) 

or

Frame.BackgroundColor3 = "Red"

or

Frame.BackgroundColor3 = 96, 200, 11

and a bunch of other methods that all fail, and I just don't get it. Can someone tell me the correct way to change the background colour of a gui

This did not work because you did not specify Frame.

Frame.BackgroundColor3 = Color3.new(255,255,255)