Jonathan,
There really isn't one god, consolidated source. But, here are several that you can use together to attempt to piece together what you have.
First, I'd be remiss if I didn't plug my
own site. Unfortunately, I don't have all of the Germania entered yet, either because I haven't yet scanned them in (pre-1919 stuff( or I don't yet own a copy (several of the color varieties). You can get to many of them using the menu system, or just type "germania" in the keyword search block,
like thisAlso, I do have a
Germania Identification Aid on my website. It only covers the basic catalog number, not the color varieties, but it will at least get you to the right base catalog number.
The German Wikipedia also shows examples of the basic issues, though not the color varieties. Here's the
1905-1915 set, but if you scroll to the bottom of the page, you can click through the years to see others. It's in German, so if you don't speak German, get ready with Google translate. After looking at a few of these, you'll get the basis of the German words that mean something -- "farbe" = "color", for example.
Once you have the basics down,
this website really gets down into the weeds. It's not terribly easy to navigate since it's just pages of scanned-in display pages, but it will give you some idea of color differences on some of the issues, etc.
WRT color differences, these are tough, since color will vary from one scan to the next, and you really need to compare the colors side-by-side. Your best bet is to go to
Philasearch. It's a website that shows auctions of most of the major German auctionhouses, and it's available in English. Click through "Browse," "German Empire," and you should see categories on the left which include Germania, and a search block to search by catalog number. If you're trying to differentiate the color varieties of a particular stamp, type the base catalog number (ex. 86) into the search block, and you'll usually get results showing multiple color varieties (ex. 86 I b, 86 I d). Since the colors can vary from scan to scan, I'd look for scans from the same auctionhouse, since it's likely they used the same scanner and scanner settings from stamp to stamp.
Finally, send me your e-mail address and I'll shoot you some additional files that will help you out.