We know that our eyes are sensitive to light labeled "visible light". These electromagnetic waves correspond to wavelength range of
Eye of Humans and of many other animals, photopic vision, vision of the eye under well-lit conditions, allows color perception, through cone cells present in retina.
The visible colors from shortest to longest wavelength are:
violet, indigo, blue, green, yellow, orange, and red. The white light is a mixture of these colors. Black is a total absence of light. Moreover Ultraviolet radiation has a shorter wavelength than the visible violet light and Infrared radiation has a longer wavelength than visible red light.
if we observe Eye Color sensitivity chart reproduced above we see that Violets which have wavelengths higher than ultraviolet and reds which have wavelengths lower than infrared are the colors of light which are least visible to human eye.
Under low light conditions survey revealed that Dark red is hardest to see.