Have you ever wondered what are the four colored dots at the bottom of the Newspaper?
You all have read newspaper a lot, or even if you have just piled up a bundle to hand it over to a raddiwala, you must have noticed that all newspapers have 4 coloured dots/hearts/squares at the bottom or on the edges.
Those four colors — cyan, magenta, yellow black (known as CMYK in four-color process printing) — are the base colors for creating all the colors you see in print. Basically any colour can be obtained by using these in correct proportions.
They are each laid on the page separately by individual plates or films. To print a crisp and accurate full-color photo, the four plates/films, must be lined up on the page in the same spot (you will often see what looks like a plus sign in the registration marks as well, and this is the guide used to line up the corners of the plates/films).
In case of a blurred photo or off color (too red, too yellow, etc), we can easily look at these registration marks and know which of the color was aligned or printed properly.