It is built using the same logic I applied in https://github.com/collectd/collectd/pull/499, I went ahead with it since it was met with a lot of enthusiasm, I did not take into account the fact that stacked graphs would look funky.

I guess the active bit can be backed out. My preference would be for it to be an option which I can add to this PR for people still needing it, would that be alright with you ?