E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
City of the Violet Crown.
Athens is so called by Aristophans (oεosee Equites, 1323 and 1329; and Acharnians, 637). Macaulay refers to Athens as the violet-crowned city. Ion (a violet) was a representative king of Athens, whose four sons gave names to the four Athenian classes; and Greece, in Asia Minor, was called Ionia. Athens was the city of Ion crowned its king or of the Violet crowned. Similarly Paris is the city of liliesi.e. fleursde-luce or Louis-flowers.
I do not think that Athens was called oεo from the purple hue which Hymettus assumed in the evening sky.