The "printable version" link (adding printable=yes to the query string) is meant to activate the print stylesheet for on-screen display.
On the Modern skin, this isn't working correctly. While many UI elements correctly disappear, the background, borders, sidebar, fonts etc are still all there as the on-screen display.
An actual print preview shows a nice spare "print look", which may indicate that this skin is using its own @media print overrides.
(Tested in Firefox 3.0b5)