White silk is how they used to do it, or it was converted from an Eagle.
When I go to edit your part FZ says it can't do separate copper layers, but when I looked at the XML it looked fine except for the text. I cleaned it up and no error now.
Unzip this one and open the pcb and look at the Ink's XML edit tree and open up silk and copper groups, then compare it to your svg EDIT/XML Editor tree.
VALOR PM6078-04 DC-DC Converter.fzpz (7.8 KB)
Ink has a bug sometimes when I indent nodes in XML edit tree where sizes change, so I didn't check those as this was just and experiment. If you want to check them you might be able to use the svg.