Dreaming of a black or brown rat is a sign of illness or treachery ahead.
In European tradition, rats are associated with theft of foodstuffs and the spread of disease, and therefore seeing brown or black rats running free is a warning to see your doctor and to be careful whom you trust.
Seeing brown or black rats in cages, however, is a sign that small irritations in your life will be dealt with. Catching a rat in a trap indicates freedom from worry and a release of tension.
White rats, on the other hand, are a sign of protection from beneficent forces or entities around you.