I found this blue hat at a thrift store and fell in love with the shape/fit, but I hated the color. I wasn't sure if dyeing it was a bad idea or not but I figured it was worth a shot. Here's a quick overview of how I did it in case anyone wants to try.
What you'll need: a hat made of natural fibers, Rit fabric dye, rubber gloves, and a bucket large enough to fit the hat comfortably.
My hat was wool felt so I made sure use water that wasn't too warm. I left it completely emerged in the water for about half an hour, making sure that the shape wasn't being compromised.
When you take it out to dry, it's important to make sure it's in the proper shape. It will probably take a long time to dry. I left mine out for about 48 hours making sure it was completely dry.
It turned out this really great gray/purple color. I really, really love it.
Good luck if you decide to try this! Sorry my instructions aren't the best, haha.