Reduce ASB values.json size by replacing color set entries with indexes

[coldino]

Indexes can come from the existing local colour table, but we will also need to support color names from other mods and/or the core game. Suggest adding a new entry at the top-level for color lookups.

This will require a bump to "format" version number and notification @cadon before it goes live.

Should probably only be implemented after #94.