This is the most "why is this on the front page of HN?" post I've ever seen.

Some AI slop to let you pick any color and brightness: https://codepen.io/zamadatix/pen/VYerweP. Note: it does not attempt to clamp anything, so if you extend brightness beyond what makes sense in the color space or your display can't actually represent that color the color may shift. If things just appear white try lowering the brightness (and checking it's actually running in HDR at the bottom).

If you have an HDR monitor + the latest Chrom* based browser this should work out of the box on macOS/Windows. Other platforms/browsers you'll have to check the WebGPU + HDR standards support (which will be different for <canvas> than <video>) and may need to twiddle flags and/or wait for future releases.

It should tell you the active color space and range info at the bottom.