The normal human eye has over 125 million light sensors, split between rods and cones at a ratio of approximately 20:1.
The rods are significantly more sensitive to intensity than the cones, but the rods only perceive light as shades of grey. Whilst they cannot determine color information they respond best to the low frequency light at blue end of the spectrum. Therefore our eyes are most sensitive to intensity changes in blue light.
The cones in the human eye are sensitive to color across the full visible spectrum with the highest level of sensitivity around the green/yellow area. Therefore our eyes are most sensitive to color change in the green/yellow part of the spectrum.
In low light situations the rods work best and therefore color perception is reduced. The color sensitive cones work best in high light situations.