personally I'd go for yellow
yellow lighting affects your nightvision less, lights up wet roads better, and works better in foggy/rainy/snowy conditions
but from your two options.. white or blue..
i'd say white.. or stock amber
reason I wouldn't go blue well if it shines blue.. Blue light also shifts the color hue of everything on the road to blue scale, which fatigues your eyes more than a standard halogen bulb, and it's brightness isn't that much of a marked improvement over a xenon-filled halogen bulb.