i have same issues, i just edit my white logo and insert dark background in white invoice or quote
default in invoice & quote will use logo from General setting >> Logo URL
but u can custom logo by edit viewquote .tpl
dont forget edit quotepdf.tpl too, if u edit above
upload and change directory
# Logo
if (file_exists(ROOTDIR.'/assets/img/logo.png')) $pdf->Image(ROOTDIR.'/assets/img/logo.png', 20, 25, 75);
elseif (file_exists(ROOTDIR.'/assets/img/logo.jpg')) $pdf->Image(ROOTDIR.'/assets/img/logo.jpg', 20, 25, 75);
else $pdf->Image(ROOTDIR.'/assets/img/placeholder.png', 20, 25, 75);