Formatting for tables change when users print a page online

Hi,

I have a Webhelp system created with Robohelp 2015 that I recently added a print button to, but I notice that table formatting changes on the printed document (cell colors disappear, line width changes, etc). The same issue occurs if I use the browser's (either IE or Chrome) print feature. Using the Printed Documentation feature in Robohelp itself yields the correct formatting.

Any idea what could be causing this?

Thanks,

Greg