Our Relay used to use brown and white. Brown were "in memory" white were "in honor" 2 years ago they changed. I missed the brown bags, because I felt that it made a bigger impact to see the different brightness of the bags.

I was informed that the policy changed and our division was only using white bags from now on, because they wanted to keep the message hopeful.

I don't know about other colors of bags, but that is what I was told last year. You may want to check with your ACS staff partner or event chair.