Is there a scriptural and/or historical reason why priests wear those white collars? When did that start and why?
When Jesus speaks to the Church at Sardis through John (in Rev. 3), he says:
White is typically a sign of purity, such as when Isaiah says:
Having a white collar is like having a yoke of purity around your neck. It is a symbol of the obligation that priests have to model God, and the literal stranglehold (yes, they suck!) God has around us, when it comes to modelling purity.