I have an X and with True Tone off, my device is definitely cooler. I only have it warm at bedtime so that I have an easier time falling asleep if I was using my phone before bedtime.
Feels like a lottery! I went through four XS Maxes and all had warmer/yellowy displays that I was not happy with. I gave up. However, just picked up a Red iPhone XR and the display is PERFECTLY cool! Nice crisp white. Finally!! Haha. I am very happy.