Dina Kraft has written a really interesting article in the New York Times about the discovery of a 2,000-year-old textile thought to be an example of tekhelet blue. While tekhelet blue is usually thought to be sky-blue, this new research suggests that it is in fact a bluish-purple.
The whole article is worth a read, but I especially liked the quote from Dr. Zvi Koren, the researcher who discovered the dye; in addressing the change of symbolism this colour-shift might indicate, he said, “It’s not the color of the sky as we know it; it’s the color of sky at midnight. It’s when you are all alone at night that you reach out to God, and that is what tekhelet reminds you of.”
You can read the whole article here: http://www.nytimes.com/2011/02/28/world/middleeast/28blue.html