How do digital color cards work?
The color cards have an open space in the middle of the card. To determine the color of an object the open space needs to be placed on top of the object. Then a picture is taken of the complete card to capture the color of the object as well as the surrounding colors on the card.
The idea is that the surrounding colors will help to determine the color of the object. Without balancing out the color measurement process with the surrounding colors on the card, color fidelity—the color quality of the colors captured by the smartphone only— would be very low.
As we do not know the actual algorithms involved in the Apps of TechKon and XRite we had to come up with one of our own. A very simple one just for fun.