It is a lovely, rich shade of purple, and I have struggled to photograph it. If you average out these two in-progress photos, you'll be close:
The yarn escaped from its ball band long ago, but I suspect it may be Araucania Ranco. The pattern is Summer Wind (that's a Ravelry link, so if you're not on Ravelry, I don't think it will work). Beautifully written, and I will make it again. I expect to finish this cowl this weekend and will then struggle some more with photographing purple to show it to you in its final glory.