Thanks, Gary. Yeah, the purple on the plume was a bit of a leap. But I had posted some questions over on the MedRom forum before I started and here's what one of the experts there said:
"The only real evidence we have for the clothing colours of gladiators are the mosaics, especially those from North Africa, e.g. the huge number in the museum at Bardo in Tunisia. There are limitations, of course, depending on the colour of the stone available - but the predominant colour (at least of those that fought the wild beasts) seems to have been white, with coloured stripes.
We also know that the chariot teams wore colours, white green, red and blue - at least in Rome itself. There were obviously many more gladiatorial schools than four, but I can't find any evidence that they favoured one colour over another.
I do think that Gary may have a point, though. Yellow was a very peculiar colour for the Romans. It was not only the colour worn by the Vestals but it was also the colour of the veil that a bride wore to her wedding. This might have made it highly unsuitable for a gladiator to wear. Possibly also for the use of purple - although I think that there would have been no bar to using this as a colour for helmet plumes as we know that this was done in Republican times.
Dr. Mike"
So purple feathers are probably okay. While the gladiator was a slave, their owner could have used purple as a display of his wealth. And emperors owned gladiators so maybe this is one of theirs. But, yes, before I heard from the experts over at MedRom I had thought purple was a color I should avoid.