The docs for GD say that GD::Image->trueColor(1) is for backwards compatibility and also that it needs to be done before creating new images.

I have a feeling you'll want to ditch that option altogether and specify what type of new image you want with something like:

my $blank_rgb_image = GD::Image->newTrueColor( $width, $height );
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or

my $blank_palette_image = GD::Image->newPalette( $width, $height );
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explicitly.

I've never tried to get the package-wide palette/truecolor option to work in new code, since GD.pm has offered specific methods for both for quite a while now.

You'll probably also want to get rid of the indirect object syntax in your code. It my not bite you now, but it's better to get into a habit of using direct syntax and not worry about it. In case you're wondering what that means, change for example:

my $foo = new GD::Image;
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to

my $foo = GD::Image-new;
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which does not suffer from the type of ambiguous parsing of the former.