If you want to use a red area on a percent scale, make it based on the input limit of the pressure regulator. And I would still prefer psi on the scale there to permit overpressure later without UI changes.
100% propellant load at reference temperature 293K would be equal to 4500 psi
5000 psi would be equal to 111% or a temperature of 325K (~50°C)
If there is a higher temperature limit, we would need a larger scale:
100°C ~ 373K => 5700 psi @ 100% propellant mass
But that exceeds the proof pressure of the pressure regulator valve, which is 5400 psi. (Burst pressure of the valve is 7800 psi, a lot of other things would have failed first by then).
The green range for the pressure would be 350 to 3600 psi.