PHP Function for converting MC colour codes to HTML

parseMcTxt.php

function parseMcTxt($inputTxt){
  $inputTxt = str_replace('||', '<br>', $inputTxt);

  $split = explode("&", $inputTxt);
  $output = "";
  foreach ($split as $key => $value) {
    $color = substr($value, 0, 1);
    $str = substr($value, 1);

    $span = "<span style='color: ";
    switch ($color) {
      case '0':
        $span .= "#000000";
        break;
      case '1':
        $span .= "#0000AA";
        break;
      case '2':
        $span .= "#00AA00";
        break;
      case '3':
        $span .= "#00AAAA";
        break;
      case '4':
        $span .= "#AA0000";
        break;
      case '5':
        $span .= "#AA00AA";
        break;
      case '6':
        $span .= "#FFAA00";
        break;
      case '7':
        $span .= "#AAAAAA";
        break;
      case '8':
        $span .= "#555555";
        break;
      case '9':
        $span .= "#5555FF";
        break;
      case 'a':
        $span .= "#55FF55";
        break;
      case 'b':
        $span .= "#55FFFF";
        break;
      case 'c':
        $span .= "#FF5555";
        break;
      case 'd':
        $span .= "#FF55FF";
        break;
      case 'e':
        $span .= "#FFFF55";
        break;
      case 'f':
        $span .= "#000";
        break;

      default:
        break;
    }
    $span .= "'>" . $str . "</span>";
    $output .= $span;
  }

  return $output;
}