$color = new Color('black', 'white');
echo $color->apply("foo");
echo "\n";

$color = new Color('red', 'yellow');
echo $color->apply("foo");
echo "\n";

$color = new Color('#000000', '#ffffff');
echo $color->apply("foo");
$color = new Color('#000', '#fff', ['underscore', 'reverse']);
echo $color->apply("bar");
echo "\n";

function rainbowColor($i) {
    $h = (int) ($i / 43);
    $f = (int) ($i - 43 * $h);
    $t = (int) ($f * 255 / 43);
    $q = 255 - $t;

    if ($h == 0) {
        return new Color('', sprintf('#FF%02x00', $t));
    } elseif ($h == 1) {
        return new Color('', sprintf('#%02xFF00', $q));
    } elseif ($h == 2) {
        return new Color('', sprintf('#00FF%02x', $t));
    } elseif ($h == 3) {
        return new Color('', sprintf('#00%02xFF', $q));
    } elseif ($h == 4) {
        return new Color('', sprintf('#%02x00FF', $t));
    } elseif ($h == 5) {
        return new Color('', sprintf('#FF00%02x', $q));
    }
}

for ($i = 0; $i < 128; $i++) {
    echo rainbowColor($i)->apply(' ');
}
echo "\n";

for ($i = 255; $i >= 128; $i--) {
    echo rainbowColor($i)->apply(' ');
}
echo "\n";