I'd go with red, as blood is red, and spilling blood is my thing... and being a lightsaber it would kinda evapourate most of the blood that i would prefer to be flowing and spraying... so I'd hafta get the colour in there somehow, wouldn't I?
also I would be spectrally neutral only killing if directly provoked in such a way as it would be required as an action... I do not feel strong enough emotions to be a sith, and yet I'm not one to sacrifice myself too easily either, and almost all the stuff i would want to do with any powers therin would be against the jedi code... so yeah...
My choice of colour is theatrical at it's core. after all when you kill someone, you want it to have a strong effect, after all killing itself is a strongly symbolic act, may as well strengthen the symbolism... and red is a perfect colour to do that with.