I am a new Aperture user. Color labels seemed intriguing but no immediate use came to mind.
I am working on a large project (1700+images) and began by breaking it down into geographical regions (a long trip around Mexico). I continued to refine but I do have numerous images that have some relevance to each other throughout. I began to stack them and copy them to albums where I work on them. It got confusing as to which stacks I had copied so I began to color the pick red when I was ready to move the stack.While working on a stack I color the pick yellow and the next picture to be worked on yellow. Once I complete all the adjustments in the stack I change the color to green so that I know it's done. I can now instantly assess my progress both in the album where I'm working and in the Project. It also allows me to locate and isolate all my stacks in the Project with a filter.