No, I did it all indoors, and in my kitchen as a matter of fact. I have no choice, at least for the mixing, immersion part. It did not make a big mess, I had a bucket in one sink, the bowl in the other, another bucket of cold water on the counter to rinse my gloves, and another area beside the sink to work on, covered with a dollar store plastic tablecloth. ( I taped the table cloth just under my window, so that any splashes wouldn't get on the wall.) That work space is just a bit bigger than your standard dish drainboard/rack. As I put each piece into a beer cup with dye, it went into a dollar store kitty litter tray, sitting on my stove top. Beside my workspace.
Ideally, this would be done in a laundry room, or garage with running water. I don't have a laundry tub (yet), so kitchen it was. But I was masked when mixing the powder (N95 masks are everywhere now due to Swine Flu), and had my kitchen window open. I did find the blue dye was unappealing in smell, and the odour of the soda ash is yucky, but I kept that to a minimum (got rid of the solution as soon as done. I would recommend good ventilation when rinsing, or else wear a mask. And ALWAYS rubber or latex gloves.