I’m glad you showed the red/black red/white issue there and would like to know a bit more about the methods. For insight, when I was taught color theory, I learned that color is built from three properties:
Tone: The amount of black in a color.
Hue: The color without tone or saturation taken into account.
Saturation: The amount of pure color regardless of hue or tone.
So for instance, your red example has ~10% tone (10% black), with an almost pure red, but a very low saturation of red. This means that the color is acting more like a gray than a red, and because it’s hue level is very high, that in combination with the tone makes the color act more like a 60% gray.
When you see it like that, it’s obvious why white stands out more than black. Can you comment on that and whether those theories are present in your measurement?