Interesting - thank you for teaching me more about her color! I figured "tri color = three colors" and she definitely has three different colors. So I learned something!
Actually you aren't too far off in the thinking that Tri = three colors. There are three colors, black, tan and white, on a tri colored Sheltie. The difference is where and how the color appears on the dog. Here's the official American Shetland Sheelpdog Club's (ASSA) description of a Tri:
http://www.assa.org/Tri.htm Basically you have a black dog with a little tan on the face, legs and butt. White will normally be on the collar, chest, legs and tail tip. Unlike the Sable where you can gradient color from light to dark on each hair, the black, tan and white are solid on a Tri. Sables also tend to have an all tan face, sometimes with a white blaze.
A Sable Sheltie actually has a range of color varieties within the Sable color category but they are all, officially, considered Sable. There are light/golden Sables, darker mahogany/shaded Sables and everything in between. Interestingly, if you look at the darker hairs, you can actually see a gradient of color from light at the root to dark at the tip. Here's the ASSA's description of a Sable:
http://www.assa.org/Sables.htm. If you look at the 2nd picture, you'll see a darker Sable like your Maddie.
If you are curious about the rest of the rainbow of colors for Shelties, they are all listed here:
http://www.assa.org/colors.html
