This is a bit like the origin of the term "boxing day". Who's right?
I have heard the theory of the titanic, but it was the band that kept playing, not the engineers, and it dosen't explain the colour purple.
I am told, and believe, that some queen gave the colour purple to the engineers corp.
Epaulettes are actually the flap of the shirt, the "SLIDE" is the striped removable fabric with gold stripes.
In a few countries, it is accepted to wear 1 to 4 gold stripes with purple bands inbetween and also a black band for the engineers having died in wartime.
I do agree that wearing multiple strips of gold are worth there weight when flying through certain countries, especially asia.