I'm a little better at showing rather than describing so I'll do a combination of both.
Tobianos typically have four white feet, white that crosses the back somewhere between the wither and the dock. The white often seems to "move" more virtically, and the pattern can also sometimes give circular edges to the white. Tobiano does not cause face white, and, when another gene puts face white on the horse, the tobiano sometimes tries to "erase" it or push it off of the face. Homozygous Tobianos often have markings known as "Cat Tracks," but the appearence of them does not garuntee that the horse is homozygous Tobiano.
This is one of my favourite examples of the circular edges that Tobiano can cause.
The smaller spots inside the white of these horses are the markings known as "Cat Tracks"
Sorry if that's a little overboard. Tobiano just has so many neat little variations
Now for Overo!
Overo is the "catch all" term used for horses with pinto white not caused for Tobiano. The Overo Patterns are Splash, Sabino, Domaint White, and Frame.
Frame Overo is often simply refered to as "Overo." White from Frame tends to move more "horizontally" than Tobiano, and Overo white does not typically cross the topline. Frame, by itself, does not seem to cause leg white below the knees, but it does seem to cause face white. A horse with frame can be soldi or nearly complely colis.
Frame is also responsible for Leathal White Overo (LWO). Foals who are homozygous for Frame are born with incomplete digestive tracks and die or are euthanized shortly after birth. Heterozygous horses are completely normal.
Is sort of a grey area Sabino is caused by many genes, one of which is testable. The testible variation is SB1 and is found most often in Tennessee Walkers. Sabino causes white with jagged edges, roaning, and seems to push white away from the eyes.
3 variations are now testable. Splash is characterized by bottom heavy blazes, white that "falls off" one side of the face, smooth edges, and horses who look like they been dipped in a vat of white paint. Splash can caus deafness, but not all Splash White horses are deaf.