I have this issue also, working on Manager / Learner dashboards. The colours are not able to be linked to the actual status, instead if the person doesn't have a value or resort themselves the colours don't move with them which is very confusing. I have resorted to is Certified Yes/No to keep it really simple.
Totara Learn Open Discussions
Controlling colors in reportbuilder graphs
Re: Controlling colors in reportbuilder graphs