But priority is already determined by location, highest priority to lowest, top to bottom, and left to right. I'm still unsure of what to use colors for.
You can use colors to denote a category, if you can easily categorize your tasks into a few groups.
You can change order. You can't change color. Reprioritizing happens.
Color's could be used to show which project it's associated with. I've been doing this with my Moleskine lately. I have a differnt color of tab depending on what project that page or section of pages has to do with.