I like BOD2 purple best out of the available choices. It's got a regal quality to it. Using a BOD color could be a logistical nightmare tho since not only would every character in the guild have to be provided with a uniform of this cloth, but replacements would need to be provided every time someone forgets to insure all their uniform pieces or is just unable/unwilling to do so. I doubt there's any chance of obtaining a "magical dye tub" for this color since it would devaluate the products of the BOD system, so if someone were to lose their uniform it could take a long time before they're able to meet with whomever holds the guild supply of purple cloth to make new uniforms.
That said, purple6 might be better to use since we can easily make a dye tub of that color available for public use.