The red clothes are MUCH older. There is a fresco image of St Nicholas in one of the cave churches in the Ihlara Valley in Cappadocia, in which he is wearing almost the same clothes as a modern supermarket Santa except for having a black cap. That fresco must predate the Seljuk conquest so it's at least 800 years old. It's captioned so we know who it was meant to be.

Maybe somebody here is familiar with the Greek iconography for St Nicholas in other places? The attributes of saints were standardized quite early on.