White armour

White armour, or alwyte armour, was a form of plate armour worn in the Late Middle Ages characterized by full-body steel plate without a surcoat. Around 1420 the surcoat, or "coat of arms" as it was known in England, began to disappear, in favour of uncovered plate. Areas not covered by plate were protected by mail sewn to the gambeson underneath.

During the fifteenth century national styles of armour emerged. White armour was a term used synonymously with Italian design, which was innovative in expanding the use of plate armour to cover joints that had been previously protected by mail. The descriptive term white armour referred both to the absence of a surcoat and the absence of decorative trimmings: the rival German style was fluted, both for aesthetic reasons and for structural advantage in resisting crushing blows.

These two approaches to armouring remained recognizable throughout the fifteenth century. Eventually each borrowed the other's innovations. By the early sixteenth century the distinction became obsolete.

Black and white armour is a different term, for late 16th and 17th century armour that uses a contrast between highly burnished "white" and unpolished "black" areas for decorative effect in large bold patterns over the armour.

...
Wikipedia