I think we're best going with a custom dye. Everything about this process is bespoke - a one off tartan set, with a unique name and provenance, for a small group of people, through the only mill capable of making custom orders - why not add customised colours which match the design?

I think it'd do no justice to the design or Artificer's vision to settle for "good enough" - the striking acid green stripes and almost pitch green background look fantastic on the PC screen, and to replicate those colours as close as we can would only further enhance the end product. This is a once in a life time opportunity - why risk hitting the mark over a couple of weeks?

I vote for custom