So, I was just wondering, like you do ...

[Cogito]

What colour do the warp nacelles on a vulcan ring ship glow? Anybody remember?

[WarpGirl]

I'm remembering purple, but don't count on that. Maybe orange???

[Cogito]

Purple is sounding credible, and is backed up by some animations on YouTube. I'll go with that for now, but if anyone knows differently I'd be grateful if you'd let me know.

[Transwarp]

I ran the warp equations assuming a space-time gradient less than 0.03, normal mass coefficient, and an annular field configuration. From that, I computed an emmission spectrum for secondary cherenkov radiation in the violet to ultra-violet range.

Of course, you'd see shorter wavelengths at higher warp, so it would only appear to be purple (violet) at speeds below warp 3.

Hope this helps.

[Cogito]

"Of course ..."!

[Alelou]

And the award for stunningly convincing technobabble on demand goes to Transwarp!

[Kotik]

*duh*