http://www.fbi.gov/hq/cid/civilrights/color.htm
It’s a federal crime for anyone acting under “color of law” willfully to deprive or conspire to deprive a person of a right protected by the Constitution or U.S. law. “Color of law” simply means that the person is using authority given to him or her by a local, state, or federal government agency.
The FBI is the lead federal agency for investigating color of law abuses, which include acts carried out by government officials operating both within and beyond the limits of their lawful authority. Off-duty conduct may be covered if the perpetrator asserted his or her official status in some way.
During Fiscal Year 2005, the FBI investigated more than 1,100 color of law cases. Most of these crimes fall into five broad areas:
• excessive force;
• sexual assaults;
• false arrest and fabrication of evidence;
• deprivation of property; and
• failure to keep from harm.
False arrest and fabrication of evidence: The Fourth Amendment of the U.S. Constitution guarantees the right against unreasonable searches or seizures. A law enforcement official using authority provided under the color of law is allowed to stop individuals and, under certain circumstances, to search them and retain their property. It is in the abuse of that discretionary power—such as an unlawful detention or illegal confiscation of property—that a violation of a person's civil rights may occur.
Fabricating evidence against or falsely arresting an individual also violates the color of law statute, taking away the person’s rights of due process and unreasonable seizure. In the case of deprivation of property, the color of law statute would be violated by unlawfully obtaining or maintaining a person’s property, which oversteps or misapplies the official’s authority.