Violet Husk

One drop with exactly one use, and Lac Beetles are the only source. They live down in the Underground Jungle, which is not somewhere you casually farm early. If you want a full set dyed the same purple, go down with a Battle Potion and a Water Candle running and clear a long stretch of tunnel, rather than waiting for husks to trickle in while you do other things.

Violet Dye is a deep purple that reads well against dark armor and holds its color in low light, which is more than several of the brighter dyes manage.