HP Print Service plugin comes pre-installed in both my Nexus 7 and Samsung Galaxy S5.
HP says that the "HP Officejet Pro L7500 All-in-One Printer Series" of printers supports "Print solution for Android and Kindle devices".
My Officejet Pro L7590 is harwired onto my network and available to PC on same LAN. My Nexus and Galaxy can see the L7590 as a printer, but the print button is grayed out and the printer is shown as "unavailable".
I have already tried uninstalling and re-installing the print service plugin on the Nexus 5.
Anything else I can do to troubleshoot?