The day subsides, the sun descends. The salt water recedes from the dunes. The sadness of the dusky purple twilight.
A monochromic image is composed of one color (or values of one color). The term monochrome comes from the Ancient Greek : monochromos - 'having one color'.
Violet is the color of light at the short wavelength end of the visible spectrum, between blue and invisible ultraviolet. It is one of the seven colors that Isaac Newton labeled when dividing the spectrum of visible light in 1672.