The frequency (color-) composition (= chromaticity) of the lighting is very different in different photographing situations. Different light sources have very different chromaticities, which produce a very different color reproduction in photographic pictures.
The more the chromaticity is different from bright daylight, the more the colors reproduced by photography seem to be just "wrong" to the human eye, cause the human brain automatically eliminates the effects of different chromaticities by some physiological color or white balancing, so that most people consciously only realize different chromaticities in color photos.
In modern digital cameras the picture which is perceived by the sensor, is processed by a complex software, which is able to perform something similar as the physiological white (or color) balancing in the human brain, cause the aim of modern color photography is to reproduce the color impression of the eye as precise as possible. Normally this electronic "white balancing" is done automatically and it gives more or less acceptable results as long as the lighting is not too different from bright daylight.
But this automatic white balancing fails regularly in difficult lighting situations. That is why today (except of very simple cameras) all better cameras offer a "custom mode" for manual white balancing. This manual mode needs external calibration tools.
mennon® offers several calibration tools for this custom mode color balancing. These innovative patented tools do not only allow a white balancing on a professional level, but also offer completely new options for creative photo compositions which did not exist before.