Well. Citation needed. This is pretty endlessly debated. You don't see many yellow fog lights or ski goggles these days, and there is a reason:
HID colour temperature
OEMs seem to go for about 4300K for HIDs, and I'm willing to bet they've done some research.
http://www.gerontechnology.info/Journal/Proceedings/ISG08/papers/036.pdf
"From this figure, it can be seen that there was no difference between color temperatures of 3100 K and that of 4700 K."
"There is no relation between visibility and the color temperature of a headlight."
Most importantly,
there are no H4 replacement LEDs that will improve visibility without impairing it for other drivers.