I updated the brilliant gallery to 6.x-3.6 and all images in the gallery got a black background. After debugging the code in the brilliant_gallery.module, I found the bug:

In the function replace_brilliant_gallery_tags(), you can find the following code:

    if (!$isnewgettag){
      // Plain old tag
      $match = $newmatch;
     }
    else {
      // OK, we've got the new generation params in $newgenmatch
      # $newgenmatch
    }

Remove or comment out the following line:
$match = $newmatch;
The $newmatch array contains the parameter with the wrong indices. Empty items have been removed and so they didn't match. The variable $match still contains the items in the right order.

See this output of var_dump($match,$newmatch); right before the if:

array(7) {  <== $match
  [0]=>
  string(2) "bg"
  [1]=>
  string(15) "a-wurf/abschied"
  [2]=>
  string(1) "3"
  [3]=>
  string(3) "100"
  [4]=>
  string(0) ""  <==
  [5]=>
  string(0) ""  <==
  [6]=>
  string(7) "#ffffff"
}
array(5) {  <== $newmatch
  [0]=>
  string(2) "bg"
  [1]=>
  string(15) "a-wurf/abschied"
  [2]=>
  string(1) "3"
  [3]=>
  string(3) "100"
  [4]=>
  string(7) "#ffffff"
}

Ciao,
Mike