Purple was a color.
Purple omelettes were made with grape juice and eggs. (TNG: "Imaginary Friend")
In 2368, Timothy claimed that the people who attacked the SS Vico in a black cluster wore purple helmets. (TNG: "Hero Worship")
In 2371, upon seeing the seas of Earth, Jadzia Dax wished they were more purple, while Kira Nerys wished they were greener. (DS9: "Past Tense, Part I")
In 2373, Molly O'Brien wore her new purple shoes for her father Miles O'Brien. A Pah-Wraith possessing Keiko O'Brien told Miles and asked if Molly looked pretty. He agreed. (DS9: "The Assignment")
Also that year, after Kathryn Janeway had apparently died, Harry Kim recalled eating overripe fruit until his hands and mouth were purple. The captain's mouth was similarly stained. (VOY: "Coda")
In 2376, after being assured by B'Elanna Torres that he'd be able to mimic the appearance of whatever species lived on Kelemane's planet, The Doctor asked what he would do if they were "big, purple blobs of protoplasm". Janeway assured him he'd be "the best looking blob on the planet". (VOY: "Blink of an Eye")