Some of the machines that PARC did in the late seventies had a three button mouse. Each button had a different colour: red, yellow and blue.
Today Squeak smalltalk uses the concepts "red click", "yellow click", "blue click" for historical reasons.
Instead of putting coloured little, plastic stickers
on each button I'd like to have a proper mouse with coloured buttons.
Part fashion statement, part in joke and handy if you're using Squeak Smalltalk.