Purpureus is a Latin word which came directly into English in the 14th century (although not a lot of English speakers say it as an adjective these days). In Latin it means “brilliant, radiant shining” or “wearing purple” or it describes the color royal purple or red. In English it just means purple! The Latin word itself was borrowed from ancient Greek world “porphyritica” which describes the kingly purple of Tyrian purple or porphyry (a deep red igneous stone of extreme hardness which could, with much labor, be made into costly sculpture).
All of which is to say purpureus is still on the books as a color—a middle range purple almost half way between red and blue (although maybe leaning slightly toward red). The hue is somewhat paler than true purple, but it is still a very regal color. Naturalists have long used the word to describe purple creatures. For example here is a magnificent Lamprotornis purpureus—a purple starling, which makes its home throughout tropical central Africa.