Default pigment rework

[Robotgiggle]

I've noticed a couple strange things about pigments recently: there's no way to get a pure amethyst color, the default pigment is copper-themed despite the fact that people hardly ever use cyphers, ancient cyphers have no baked-in pigment, and the Vacant Pigment item doesn't have a unique texture. This PR fixes all of those problems with the following changes:

• The default pigment is now a pure amethyst color (ab65eb to be specific) and can still be applied using Vacant Pigment
• The orange-and-purple spread previously used as the default pigment is now used in Ancient Cyphers, and can be applied using the new Ancient Pigment item
• Added a new sprite for Vacant Pigment so it doesn't look identical to Soulglimmer Pigment

Left is the new Vacant Pigment texture, right is the Ancient Pigment texture