Did you know that the standard lab mouse these days is black, with a nice glossy coat?
In fact, it was a black mouse that went on the space shuttle, and was used in the mouse genome-sequencing project.
The reason: Jackson Laboratory in Maine made the mouse the number-one research model, and they happened to chose a black mouse as their standard.
Mice actually come in many colors, and scientists can order something like 3,300 varieties. Each different mouse strain serves as a model for a variety of human diseases and disorders. For instance, you can get a "knock-out" mouse, a mouse that comes with a deleted gene. They also have "knock-in" mice that have a gene added in, and "transgenic" mice, where they add in genes that mice don't normally have in order to recreate human-only diseases.
To do experiments, it is crucial that scientists have a lot of mice that are all exactly the same. For this reason, mice are inbred for 20 generations, to create a colony of genetic twins. This process also gives them a very specific genetic profile, such as a model for human diabetes. It doesn't take as long as you might think to produce the mice because they can have a litter every 21 days.