I am trying to increase the number of colors in an image, but it is not working.

 $img = Image::Magick->new;
 $img->Read('../images/logo.gif');
 my $nu = $img->Get('colors');
 $img->Set(colors=>256);
 $img->Quantize();
 my $nu1 = $img->Get('colors');
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nu and nu1 remains the same- 127 in my case. Any help is appriciated.