As far as visual differences between southerns and easterns...southerns have a more up turned snout, are very small, and as far as color goes...they do not come in many different color varieties (like eastern hogs do).

Southerns typically have a gray ground color with black spots on their sides.
The dorsal pattern is black saddles divided by light peach (normally) or sometimes their is very little color between the saddles (varies with locality).........or in VERY RARE cases there will be a deep redish orange between the saddles (like mine).
The ventral pattern is typically gray with scattered black.
Also, the tip of the tail typically changes to light brown and cream colored banding.

Easterns vary tremendously with color (and sometimes pattern), but I agree...can have similar pattern and color to southerns.
In my opinion, easterns have a less saddle-like dorsal pattern. (I�m not sure if that helps.)
You really just have to study lots of pictures of the two to be able to tell them apart easily. And like I said, there are definitely some that are very hard to distinguish in a single photo.
(I can tell you for sure though...you will never seen an eastern with as red only on its back contrasting with gray and black (like the red southern that I have).

Anyway, I hope that some of that was helpful. :-)