for my $i (0..$size-1){
      for my $j (0..$size-1){
         my $a = ($i%20) > 9;
         my $b = ($j%20) > 9;
         my $c;
         if($a^$b){
            $c = sprintf("#%02X0000",$i%0xFF);
         } else {
            $c = sprintf("#00%02X00",$j%0xFF);
         }
         $USE[$i][$j]=$c;
      }
   }