TriStar state of charge (SOC) LED transitions are based on battery voltage setpoints, and provide only an approximation of the true SOC of the battery. A true SOC calculation is not performed because the TriStar does not have load current information (current drawn out of the battery). A TriStar in charge control mode (or a TriStar MPPT) can only measure current into the battery from the solar panels.
The LEDs will however provide a relative indication of how your system is performing. e.g.:
“Each day I charge to Green. At dusk it settles to Grn-Yel, by morning I’m at Yel-Red”
which may help detect problems if the LED behavior changes drastically. (charge all day and it doesn’t get out of red).