if ($colors[$num] eq $drop[0] or $colors[$num] eq $drop[1]){      
+   
        splice (@colors, $num, 1);
        $num--;    
    }
    $num++;
[download]

Just as a nitpick: I think it's better to

    if ($colors[$num] eq $drop[0] or $colors[$num] eq $drop[1]) {
        splice (@colors, $num, 1);
    } else {
        $num++;
    }
[download]

because find it's somehow dopey (for lack of a better word) to decrement just to increment immediately afterwards.
With "else" it's clear that you need to increment only if the condition isn't met.