TRIZ, the "theory of inventive problem solving," is a systematic approach to problem-solving that is said to be the next evolutionary step. According to the principle of changing the colour, porous materials can be used to absorb or reflect light, depending on the desired effect. For example, black porous materials can be used to absorb light, while white porous materials can be used to reflect it. This principle can be applied in a variety of ways, such as in optical filters or in the detection of acidity levels. By changing the colour of porous materials, we can change their properties and uses. As such, this principle is a useful tool for solving problems in a wide range of fields.