An infrared satellite image is created by measuring the thermal radiation emitted by the earth's surface and the cloud tops. That is why an infrared image is actually a temperature chart of the underlying surface. In order to simplify the interpretation of the satellite image, the original black-and-white image was artificially coloured in. Low temperatures (high cloud tops for instance) are white or light blue zones. Higher temperatures are indicated by grey zones. By using a colour scale, it is easier to distinguish the earth's surface, the clouds and the water surfaces.
Thick clouds with high tops (cold) appear very white or light blue.
Thin low clouds with relative warm tops appear grey.