Wikipedia's definitions:
Color of law refers to an appearance of legal power to act but which may operate in violation of law. For example, though a police officer acts with the "color of law" authority to arrest someone, if such an arrest is made without probable cause the arrest may actually be in violation of law. In other words, just because something is done with the 'color of law', that does not mean that the action was lawful. When police act outside their lawful authority and violate the civil rights of a citizen, the FBI is tasked with investigating. Under color of authority is a legal phrase used in the United States indicating a person is claiming or implying the acts he or she is committing are related to and legitimized by his or her role as an agent of governmental power. The phrase can refer to lawful or unlawful acts. WikipediaPolice officers often use color of law to intimidate people. The sad part is if someone attempts to fortify by asserting knowledge of real law, the officer may be so embarrassed that he was obviously violating your rights, and continue with his intimidation. Therefore one must balance being too prideful about knowing the law and your rights so as not to appear to have a chip on your shoulder. Unfortunately, cops have much discretion and can basically do what they want and face the consequences later after they make your life difficult.
Take for instance a judge who knows he has no real authority to be conducting a hearing about something completely other than what the hearing's for. Instead of objecting, the person allows the judge to so manipulate the hearing that the judge intentionally makes a statement on record that damages their case that's in another court. Under the color of law, the judge makes the person think they have to remain at the hearing, when in reality the decision was rendered and they are free to go. They are not under arrest or bound to attend the remainder of the hearing. If the person knew their rights they would simply blow off the judge and walk out. There's nothing illegal about walking out or hanging up on a telephonic hearing civil hearing.
The abuse of color of law by authorities is a huge problem in our society today. I believe it is the primary reason our civil liberties are being gradually eroded. Some authorities use people's ignorance of the laws to take more rights away incrementally to form a precedent. Others twist the issues to make it seem it's more of a personality conflict rather than addressing the real issues at hand. When an officer makes it seem you have a personal conflict with him or her, they win.