Even on 100% brightness, an iPhone Pro 13 shows the "White" text significantly brighter than the background white.

Some other interesting observations:

• If I zoom in, the over-100%-bright text fades until it blends in with the background. This is expected (OLEDs have higher peak brightness for small areas), but what isn't expected is that it seems to do it in discontinuous steps.
• If I go outside into full sunlight, the contrast between the page and text is lower. This is again an iPhone feature in action where "maximum brightness" is actually further boosted in bright conditions.
• The text takes a few seconds to reach maximum brightness. I expected it to start at full brightness and fade, but it seems to do the opposite...

I can understand why the notion programmers have that "color" is an RGB triple of 8-bit integers from 0 to 255 is so attractive. It's a simple mental model with no complexity. But to get the most out of modern displays, we have to abandon such childishly simple models. Each color channel will need to be 10 bit minimum, 16 if using linear light. Peak brightness becomes this complex many-faceted thing with per channel maximums, all-channel maximums, and variations based on both time and area!