pocketmine\level\generator\biome\Biome::interpolateColor PHP Method

    private static function interpolateColor($size, $x, $z, $c1, $c2, $c3, $c4)
    {
        $l1 = self::lerpColor($c1, $c2, $x / $size);
        $l2 = self::lerpColor($c3, $c4, $x / $size);
        return self::lerpColor($l1, $l2, $z / $size);
    }