I don't know what charts you are looking at. The colors can be whatever one chooses to use. On my charts the volume is all the same color (I use blue). If you are using Ihub charts, you will have to ask an admin what they mean as I have never viewed an Ihub chart, but I would suspect red means the majority of the volume was a decline, green an advance and blue no change, but that's just a guess.
Newly