We know for certain that Ausf F hulls were in the production line at DB at the end of the war. Photos of the ruined factory show the hulls with the guide rails for the newly-designed sliding driver's hatch plainly visible.
Although, as Jentz has stated, all Panthers issued to the last unit were still Ausf G. However, he continues;
"Therefore, if a few Panther Ausf F had been successfully completed, they would have been issued on 20 through 23 April 1945 to the II./ Panzer-Regiment 2 for the immediate employment in defense of the Berlin area."
Personally, I doubt this happened, for if any Ausf F actually made it into combat, there would certainly be one sitting in Kubinka today, or at least a record of one. There is no way the Soviets would have passed up examining the final culmination of German tank design.
Here is the publisher's review of Duel in the Mist, the book includes color profiles of the various factory applied color schemes.
http://www.network54.com/Forum/78968/message/1172813397/Duel+in+the+Mist
Additional information;
http://www.network54.com/Forum/47207/thread/1233789169/Dragon+Panther+F+question