Changing Color of a PDF page

Dear Group,

I am trying the following code

use PDF::API2;
$in_pdf = PDF::API2->open('input.pdf');
for my $p (1 .. 4) {
	my $in_page = $in_pdf->openpage($p);
	?change the color of the entire page
}
$in_pdf->saveas("DDD.pdf");
$in_pdf->end();

How do I change the whole page color (image, text, etc)?

Appreciate any pointers.

Best Regards
Dominic