To use the Rit dye I use the hottest water available from the tap (I've found that this doesn't distort the plastic, though if it's any hotter it will), and thoroughly mix in the dye. Then put the canopy in, making sure that it is fully submerged and keep it in. You can check it every 15 minutes or so to see if it is as dark as you want - the longer the darker - and you rinse it each time you remove it from the dye so that you get a true indication of the darkness.

If it doesn't 'take' on the canopy there's no problem, you are just out the couple of $ for the dye, as the dye will easily wash off with water or isopropyl alcohol.