Map application token names to positions between 0 and 1:

use PhpColor\Color\Palette\ColorPalette;

$scale = ColorPalette::parse(['#111827', '#7c3aed', '#f8fafc']);
$positions = ['900' => 0.0, '700' => 0.2, '500' => 0.5, '300' => 0.8, '50' => 1.0];

$tokens = [];
foreach ($positions as $name => $position) {
    $tokens[$name] = $scale->at($position)->toHex();
}

assert([
    '900' => '#111827', '700' => '#392a70', '500' => '#7c3aed',
    '300' => '#c1b4fc', '50' => '#f8fafc',
] === $tokens);

at() works on ordered scales and mixes adjacent stops in Oklab. Positions outside the range are clamped.

See scale sampling or ColorPalette.

Sample a scale at token positions