Charles Spurgeon Commentary Mark 15:16

"And the soldiers led him away within the court, which is the Praetorium; and they call together the whole band." — Mark 15:16 (ASV)

17. And they call together the whole band. And they clothed him with purple,

The uniform of the Roman soldiers was purple, as if to indicate that they belonged to an imperial master; so, when these soldiers, in mockery, put on our Lord the old cloak of one of their comrades, it sufficed to clothe him with the royal purple to which, as King, he was fully entitled.