I'm aware that motor run capacitors do not have any polarity, however I have a Ducati 4uF 460v cap that has a brown wire and a blue wire coming out of it. Why are these wires coloured if there is no polarity?

The cap I am replacing had two orange wires running to it, one of which was marked with a 'C' label, presumably meaning 'common'. Do I connect the 'common' wire to the blue or brown wire on the replacement cap?

 

A motor run capacitor can also be a power factor correction capacitor, which is connected directly across the mains, and that would explain the colour coding.
It is a non-polarised capacitor (because it can be connected to AC) so can be connected either way round,

 

It seems to me, a capacitor with different wires looks more attractive to buyers

 

The Ducati motor capacitor line are principally Metalized Polypropylene construction, so are non polarized construction !

 

Cut the blue wire, its always the blue wire, right? Sorry, it was just too hard to pass up. ;-) I echo the above regarding the Cap too.

 

The blue wore is considered to be neutral (common) and the brown is considered to be the hot as that is the color coding in Europe. the wire marked C is considered to be the common so connects where the blue was and the other lead will go where the brown was simple as that

 

A capacitor used as a start or run capacitor is in series with the start/run winding.
whether oil filled paper or dry electrolytic-bi-polar. 'polarity' does not matter.