But I'll give it a go.
Eggplants, pants, bad suits, shirts, ties, flowers, aliens, eyes, beams of cosmic energy, Galactus, handkerchiefs, the sky (through a red lens), bruises, prose, crayons, magic markers, paints, computer screens, bubble gum, jewels, jello (if something went wrong), cars, trucks, Barney the Dinosaur, blueberries, colored ink, stained glass, dye, dice, pictures, shirts, cups, plates, houses (if the resident is color-blind, maybe), candy
Well, truth be told, I didn't come up with anything new for the last 30 seconds of that five minute period, and I feel like I was really reaching for some of it. (Though I'd imagine that the 'reaching' was the focus of the exercise.) I wasn't so much thinking what is purple, but what could be purple. At least, that's the direction I went.
Time to settle down now, and try to get some writing done.