According to one hypothesis, the hypertensive effect of alcohol is from a chronic state of alcohol withdrawal in frequent, heavy drinkers, but there is much evidence in favor of a direct effect of alcohol on BP.
Color Perception. The properties of color which are inherently distinguishable by the human eye are hue, saturation, and brightness. While we know that the spectral colors can be one-to-one correlated with light wavelength, the perception of light with multiple wavelengths is more complicated. It is found that many different combinations of light wavelengths can produce the same perception of color. This can be put in perspective with the CIE chromaticity diagram. The white or achromatic point E can also be achieved with many different mixtures of light, e.g. with complementary colors.
Color blindness is the inability to perceive differences in various shades of colors, particularly green and red, that others can distinguish. It is most often inherited (genetic) and affects about 8% of males and under 1% of women. People who are color blind usually have normal vision otherwise and can function well visually. This is actually not true blindness. Night blindness is a difficulty in seeing under situations of decreased illumination.