Physical properties can be perceived or observed without changing the structure of matter. These are used to detect and describe matter. Physical properties comprise: appearance, texture, color, odor, boiling point, melting point, density, solubility, and polarity just to name a few.
In this case, the physical process used is boiling, which causes water to evaporate and the contents in the tea bag to become more soluble and can make the color to change. Also, the physical property of solubility relates to some of the components of the tea.