Do you remember being at the restaurant, as the waiter wrote down your order on those thin paper 2 ply forms with the little black carbon paper sheet inside of them.

If you realize, you no longer see them anymore. Why? Because as the acronym implies, NCR (No Carbon Required)

These days the paper you write on itself has the chemical for transferring what you wrote on the top page to the sheets below without the need of the famous carbon paper.

NCR paper
was invented by two chemists working for the NCR Corp. as a substitute for carbon papers.

The back of NCR paper is coated with micro encapsulated dye and the front is coated with a reactive clay.

When the NCR paper is written on with a pen or printed with a dot matrix printer, the pressure from the point of the pen causes the micro capsules coated on the back to burst spilling the dye onto the front of the sheet below making contact with the reactive dye and therefore creating a mark.     
NCR paper is available in many different colors and what coating each sheet gets depends on the order and number of parts in the NCR Form.

For example, in a
 3 part NCR paper

White CB (coated back): 
The 1st sheet is normally white in color and does not require a clay coating on the front since it will be written on directly. The back is coated with the micro-encapsulated dye in order to transfer to the second sheet.

Yellow CFB (coated front and back): 
The second NCR sheet is usually yellow (canary) which will be coated with clay on the front to react to the dye from the back of part 1 and also coated with the dye on the back in order to transfer the writing to part three.

Pink CF (coated front):
 Sheet 3 will be pink and coated on the front with the clay coating only since it has nothing more to transfer to through the back.