Colour spectrum in technical, are visible colours from red to violet that made up the white light. They are also the reason why rainbows are so interestingly beautiful. When they are correctly applied on the web, it too gives a pleasant look.
Some credits are:
manicho, mallorcaa, SemanticOne, DJ-Takahashi, payalnic, SfinxMagnum, alsnd12, mediablade, GRlMGOR, skepnaden, iixo, Almighty-Bazaa, nathan makan, dewaynesmith, silwenka, Kamikaze00X, majinshadow, Thelma1, jugga-lizzle, Marcello