craftgrrl | dyeing polyester fabric

Does anyone here have experience with dyeing polyester fabric? I've only been able to find one sort of dye that works on polyester.

This is the dye I've found so far: http://www.dharmatrading.com/products/idye.html

I've recently purchased a dress online to replace one I had many years ago. Since the dress is no longer sold in stores, I had to settle for the only one I could find, which is navy blue. I'm hoping to make it black.

I have had one (terrible) experience dyeing polyester and it turned out awful! I was trying to go from white fabric to black. (Silly 14 year old self used Rit dye on a corset. FAIL.) Obviously, navy to black is much, much closer, but I thought I'd ask first. I'd really hate to have to disassemble this new dress to use as a pattern for a black version.

So if you have experience with this brand of dye, please let me know how your project turned out!