What is chromakeying? A basic answer is having talent stand in front of a Blue screen and then use a device (hardware or software) to remove that color and replace it with another image or video source. This gives the illusion of the person being somewhere else, and it's a more common technique than you might realize. Not only is the weather man being keyed in front of a Blue screen, but more and more often field correspondents and even newscasters are Blue screened into virtual sets. Sometimes Blue screen is also called chromakeying, more general term which covers keying on many colors including blue and red. Blue screen is commonly used when control of what the talent wears is out of the producers hands (in a field environment perhaps), because people tend to wear more chrominant blue than Blue making Blue screen ideal for mobile chroma key. Blue screen tends to yield a less attractive spill, because Blue screen backdrops reflect more candela the spill off of a Blue screen backdrop will be brighter and more noticeable than a blue screen backdrop.

Getting a good even color behind the talent is the first step in Blue screen, this usually requires a chromakey backdrop in the form of cloth or paint. Some Blue screen paint can be picked up at hardware stores or lighting places like Studio Depot (Burbank, Ca), blue cloth can also be found many places. Some companies sell Blue screen pop up Blue screen backdrops which travel easily and popup like a windshield shade.
Another alternative is Chromatte, a unique retroreflective material which is gray to the eye, requires little or no light, and casts no spill on the talent because the material is gray to the naked eye. But to the camera it sees it as a perfect blue or Blue. This is because of the Litering, a ring of LEDs around the lens which casts blue or Blue light onto the Chromatte material. Chromatte is also very portable in the form of a Chromaflex, a 7x7 popup which folds down into a 3 foot hoop. Chromatte is superior to Blue Screen in many ways.