like some people have said, using red lights will not reduce your night vision by much. I once spent the night at an observatory and they had red lights indoors so that when you went back outside to stargaze it wouldn't mess up your night vision. It also takes about half an hour for your eyes to fully adjust to the dark, all of which has to be restarted if you look into bright (white) light.
Horses also tend to have a longer adjustment time to dark light, their eyes are mainly for daylight and dusk/dawn use. If you suddenly use bright lights your horse will take longer than you to get back the "night vision." that said, they still do see better than us poor humans in the dark. I think adding red lights to the breastplate or maybe your helmate is a great idea for night trail-rides.
Moonlight is also awesome... has anyone noticed that your shadow is MUCH sharper in the moonlight than in the sunlight? It's really cool!