why do they use white rats for exsperiments?

Question

why do you see scientist use white rats for exsperiments for human disecesis instead of colored rats

Answer 1

White lab rats were first bred around the beginning of 20th century, after example of white albino mice (which are much older - some were used in mysteries of ancient Egypt) because white albino mice were known to be more docile and less stressed-out than wild ones. Wild brown rats are too unaccustomed to humans, bite and jump at every noise.
Of course, experiments on genetics of coat and eye color require albino animals (this was another major reason).
Moreover, when white animals are used, it is easier to track hybrids (from time to time, a wild rat or mouse may get into the animal facility).

Answer 2

Main reasons for using rats:
small and can be kept in relatively small areas
very similar to humans on many levels (from DNA -> cell -> tissues/organs and even up to some more "primative" psychological phenomenia like learning)
easy to bread
cheap to keep

However, contray to what many people think, I do not believe that white rats (or any type of rat) are used all that often. Yes they are used in many experiments, but more common is Mus muscus (house mouse), especially in biological experiments. Mus muscus is one of the six "model organisms" and the only mammal one.

Answer 3

I have no idea but my guess would be maybe because they don't have the color pigmentation like colored rats do so they can see if there is any skin irritation