I think the color purple is considered regal because whatever the dye used to be made from (crushed marine life or something like that) was very expensive. So if you had purple, it meant you were rich. It would be kinda funny if blue things became a sign of wealth because of this.
So it's worth pointing out that Tyrian Purple was an exceptionally long lasting dye; it did not fade when left in the sun, or after washing. Compared to other purple fabrics, Tyrian Purple fabrics always looked brand new, and I suspect that this is the real origin of their high-status associations.