Not knowing the year of your car, I'd likely not trust the temperature gauge (unless you have bypassed the compensation board). I have a 3 row Nissens in my 245, and I run the coolant level at the upper mark when cold, realizing that the level may increase as the coolant heats up. I'd recommend staying with the original color cap. You should not need to increase the pressure.

I live in Central Florida, and I use the Nissens radiator, the tropical fan clutch, the pusher fan, a 92 degree thermostat (C), and the belly pan, and air ramp are in position. Mine uses the Black cap.

Mine is a pre-compensation board car (1985) and I never see the gauge past the 8:30 position.