Blue–green distinction in language "azul-" means turquoise-blue. One can also make the distinction between "verde-claro" and "verde-escuro", meaning light and dark-green respectively, and more distinctions between several qualities of green: for instance, "verde-" means olive-green and "verde-" means emerald-green. Cyan is usually called "azul-celeste" (sky blue) or "azul-", meaning pool blue, but also less commonly "", and "verde-", meaning water green. Romanian clearly distinguishes between the colors green (') and blue ('). It also uses separate words for different hues of the same color, e.g. light blue ('), blue ("albastru"), dark-blue ("bleu-" or '), along with a word for turquoise (') and azure ('
Green light source typically has a spectral power distribution dominated by energy with a wavelength of roughly 487570 nm. Human eyes have color receptors known as cone cells, of which there are three types. In some cases, one is missing or faulty, which can cause color blindness, including the common inability to distinguish red and yellow from green, known as deuteranopia or redgreen color blindness. Green is restful to the eye. Studies show that a green environment can reduce fatigue. In the subtractive color system, used in painting and color printing, green is created by a combination of yellow and blue,