Tie Dye Help!!!!!!!!!!!?

I have been tie dyeing a while now but a couple days ago i purchased some rit dye, soda ash and cotton shirts. My creations are beautifully colored, even when i open them. The problem is when i take them out of the wash they are not as bright and the once extremely bright yellow and oranges fade almost completely. i only use cold water, no soap. What am i doing wrong? is it possibly i have to wash them with the rubber bands on? Or maybe they have to stay in their bags longer than 24 hours? please help!!!!!!