I just complained that color inputs couldn’t deal in P3 colors. Looks like Safari is the first-mover on supporting that, as well as alpha:
<input
type="color"
value="oklab(59% 0.1 0.1 / 0.5)"
colorspace="display-p3"
alpha
>Code language: HTML, XML (xml)
I was able to make a quick demo and see it on iOS:

Under the Sliders tab, it’s still just R G & B, but it seems to me you can produce colors still in the P3 space. And if you’ve set the color space, it gives you a P3 hex code there (which I didn’t even know was a thing honestly). The actual value that you get is like: color(display-p3 0.921957 0.31855 0.969179). Which I guess is fine? Just don’t expect to get out a color in the same format you put in.