It's a trick of the light. It's actually very definitely navy and that photo is AFTER I removed some red. The iPad made it royal purple
It's also just a regular heavy cotton weave of some sort. Whatever Ikea sells as their curtains. I've had it for ages. I know the velvet of which you speak but I don't know where to get it. Most velvets are velveteen these days, so they stretch. You don't want stretch for a puzzle box.
As for the OT, it's not like I've ever taken a thread OT...