Diamond Subpixel Arrangement Simulator 3 years ago
The screenshots shown in my post were from an older version. The current version should work correctly.
The purple tint was coming from naïvely multiplying the red and blue channels by 2 to try and compensate for the fact that you have half as many subpixels of R/B to work with as compared to the green channel. My new approach cuts the maximum green brightness (after converting to linear gamma) instead.
https://rickyromero.com/tmp/diamond-happy-mac.png
I stood pretty far back from my laptop's screen and it looks more accurate to me now :)