Satellite imagery is a top down depiction of clouds over the chosen surface area. Infrared imagery is not simply a photograph of the clouds from above, but rather a reflection of cloud top temperatures.
The infrared wavelength relates very closely to temperature. The interpolation of infrared waves has been used in nightvision goggles, and the concept is not much different with infrared satellite, though inversely related. Generally speaking, on an infrared satellite, the brighter colors relate to colder temperatures.
As these are top down reflections, the imagery is compiled from cloud tops, under the assumption that colder temperatures mean higher tops. As a result, one can interpret thunderstorm tops from these images during the day time, or can provide the primary satellite image overnight, when the skies go dark. Another use of infrared imagery is extrapolating snow cover under clear skies, again, owing to the change in temperature between snow and bare ground.
Because the imagery is not a true picture, but rather an interpreted image, a wide variety of colorized images are available, with different scales depending on the resolution desired, or time of year. One such example is seen below.