3. Blue:
In a research which included testing of the impact of different wavelengths of light on the human circadian rhythm, it was observed that the light wavelength which lies within the range of blues has the greatest ability to reset the biological clock, whereas there was a significant decline in that associated with greens, and a mild boost in that of red.
Moreover, blue color is used to stimulate the feelings of peace in the mind. It is also considered to be a meditating color.