The colour for engineers on epaulettes is Royal Purple as a tribute to the engineers that went down with the Titanic.
Nonetheless, King George V decreed engineering officers ever after would display their gold braid epaulets upon a "royal purple" background as a memorial to the Titanic engineers. This is a quote from a website.
http://encyclopedia.laborlawtalk.com/RMS_Titanic If you bumped into any engineers from the large airlines, I'm sure they'd be able to throw some 'lettes your way.