Re: Good on him for standing up
Purple used to be the most difficult, and therefore the most expensive
Aye - made from the shells of the Murex shellfish found along the Mediterranean coastline. I takes a *lot* of shells (and some fairly nasty processes) to make the dye.
Which is why royalty from the Phoenician kings onwards (and up to the current day, even though artificial purple dyes have been available for centuries) use purple as their signature colours (and wearing an all-purple robe/toga in the days of the Roman Empire was effectively a short-cut to a quick flight off the Tarpean Rock unless you happened to have enough legions to back you up).
Here endeth the (slightly expanded) history lesson.
 Senators has a purple stripe along the border of their tunics and togas to signify their status.
 The standard means of execution for traitors until they started to get more creative..
 Or, in some cases, just the Praetorian legion would do.