As I've managed to shoot myself in the foot as quizmaster, I'll re-type the worked answer I had given a few posts ago and meekly vacate the floor.
The sequences of colours represent
resistor values from the common E24 series. These match TOPS classes.
Orange-Blue-Brown = 360 Ohm = Class 360
Yellow-Orange-Brown = 430 Ohm = Class 430
Orange-White-Brown = 390 Ohm = Class 390
Brown-Grey-Brown = 180 Ohm = Class 180
Red-Red-Brown = 220 Ohm = Class 220
Brown-Green-Brown = 140 Ohm = Class 140
There are several potential odd-ones-out in that list, so i'd decided I'd accept any valid argument: The Class 140 consists of only one unit, the 390 is the only one never allowed to run at it's top speed (140mph), the 220 is the only diesel-electric, etc... Unfortunately I managed to misread backontrack's post earlier and prematurely declared a victory.
(And then while typing this my computer went and crashed on me!)
A Challenge has given a valid answer, and also deserves the moral victory, so over to you.