The cause of exhaust bluing is usually a lean running engine, exhaust that has been overheated, or simply a cheaper single-walled exhaust pipe. Removing the bluing is relatively easy, however the cause of the bluing should be investigated and repaired first. Repeated applications of the processes described below will remove the bluing, but will also eventually remove the chrome from the pipes.
Clean the pipes thoroughly with brake parts cleaner and a soft cloth. The less dirt that is on the pipes at the time that the chemical is applied, the less likely that the chrome on the pipes will be damaged.
Apply Blue Away, Blue Job, Blue Buster, or a similar product to the pipes following the manufacturers instructions. Blue Away is a liquid applied in a similar way to wax or polish. Blue Job comes as a powder, and is mixed into a paste with water. Blue Away and Blue Buster seem to work using abrasives, and repeated application will harm the chrome finish. Blue Job seems to work through a chemical process, probably using some sort of acid. Repeated applications would have the same effect, damaging the chrome finish permanently.
Clean the pipes again. All of the processes and products mentioned above end with the same step. Clean the residue from the cleaner and all other dirt from the pipes. Polish the pipes as you normally would to a high lustre.
Blue removal products can be quite expensive. Try the simplest, cheapest methods first, and then move on. Blue Job seems to be the toughest and to do the job most efficiently, but it is the most expensive as well.
Wear protective gloves when using products that work by chemical reaction. These are often acidic and can burn or damage your skin if contact occurs.