As the White Lambskin as the badge of a Mason, so is the regulation cap a badge of the Scottish Rite Mason.
A purple cap indicates that the wearer is a 33* Sovereign Grand Inspector General and an active member of the Supreme Council.
A white cap indicates a 33* Inspector General Honorary
A red cap means 32* Knight Commander of the Court of Honor (K.C.C.H.)
A light blue cap (or a blue 50 year pin) means that the wearer has been a Scottish Rite Mason for 50 years or more.
A black cap indicates the wearer has attained the 32nd Degree.