I tried that but it didn't work. I got it to work like this. This made the window color the same as the tabstrip color.

use Win32::GUI;
    my $main_class = new Win32::GUI::Class(
        -name    => "temp_Class",
        -color  => 16, 
    );


    $Mainwin = new Win32::GUI::Window(
          -background => "red",
          -left   => 612,
          -top    => 15,
          -width  => 400,
          -height => 455,
          -name   => "Mainwin",
          -text   => "Window Title",
          -class  => $main_class
          );
    $Mainwin->Show();
Win32::GUI::Dialog();
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