I'm not sure if the Panzer Colors are still in print, unless they were recently rereleased. I found them used a few years back, they're okay and you'll find some interesting stuff in them, but I wouldn't trust them as a definitive reference, it's more of a pile of pics.

It really depends on your interest, but if you're looking for Tigers, any of the Schneider Tigers in Combat or the Restayn books, Western and Eastern Front are excellent resources as well as Jentz' Germany's Tiger Tanks.

For general German references, you can't go wrong with any JJ Fedorowicz books, although they are pretty pricey, more like textbooks @ around $80-100 new. I'm about to put my copies of Operation Citadel up for sale to finance my next Tamiya. Fortunately, you can find some of them as Stackpole editions now, Like the Wittmann book. Their Combat histories are great for ref pics and some harrowing stories directly from the sources, I have the 503, 507 and 508. Funklenkpanzer is a beauty if you're interested in Goliaths, Borgwards and other nasty explosive stuff.

Schiefer books are sort of hit and miss, you can find exhaustive references mixed in with crap.