Write a Display P3 color with an sRGB fallback

Emit a broadly supported sRGB declaration before a wider-gamut Display P3 enhancement.

Write the sRGB fallback first, then the Display P3 declaration. Browsers that understand the second declaration use it; other browsers retain the first.

Derive the fallback deliberately

This Display P3 red lies outside sRGB, so reducing it to hexadecimal changes the available gamut:

use PhpColor\Color\Color;
use PhpColor\Color\Colorimetry\Gamut;

$wide = Color::parse('color(display-p3 1 0 0)');

assert(false === Gamut::isInGamut($wide, 'srgb'));

$fallback = $wide->toSrgb()->toHex();
$enhancement = $wide->toCss();

assert('#ff0000' === $fallback);
assert('color(display-p3 1 0 0)' === $enhancement);

Emit both declarations

Keep the fallback and enhancement in the order the browser must evaluate:

printf(
    ".brand {\n  color: %s;\n  color: %s;\n}\n",
    $fallback,
    $enhancement,
);

PHPColor converts colors; it does not generate fallback pairs automatically or determine browser support. Check the final component in both gamuts, including contrast. Continue with precision and gamut, format CSS colors, or preserve a Display P3 token.