Not all newer lenses look purple or green. Some look predominantly gold or magenta,for example.
If you look at a reflection of a bright light on any multicoated lens, you will see multiple reflections of different colors, though one may seem to predominate. Those colors correspond to wavelengths or combinations of wavelengths of light reflected back by the coating layers on the lenses. The layers, by property of their specific thickness, reduce reflections in a range of wavelengths, and light outside that range will be reflected to a greater degree, giving the color. As already stated, the coatings have no actual color.
Manufacturers sometimes tweak their coatings, too. I have optically identical Pentax "A" and "M" lenses which show different predominant colors.
I remember one guy over on P.nut who wrote very authoritatively and at length on the subject of coatings, explaining that dyes were introduced to balance color rendering of the lens. He also once said the focal length of a lens could be measured directly from the surface of the rearmost element. He got quite snippy when challenged on his claims. Guys like that don't seem to last very long here.