unfortunately in Filemaker reigns the Ford principle: "Any customer can have a car painted any color that he wants so long as it is black".
Say you have an industry standard, where let's say left = blue and right = red. A specific blue and a specific red.
Well, Filemaker does not care. You have to choose your graph colours from a limited, stupid palette of predefined colours.
You can't define your series 1 as being blue (with RGB input of values) nor you can do it for your series 2..
It's one of the main, very reasons I use a plugin for graphing.