This very common question is often well-meaning but can at times limit one’s understanding of weathering of materials. It’s like asking if someone is interested in a car or a vehicle - a car is a type of vehicle, but not every vehicle is a car. Likewise, color change is a type of polymer degradation, but not all polymer degradation is color change.
The general term polymer degradation refers to any change in properties—tensile strength, color, shape, etc.—of a polymer or polymer-based product, under the influence of one or more environmental factors such as heat, light, water and/or chemicals. Sometimes these changes in properties are also referred to as "aging". Various mechanisms, including photo-induced degradation, thermal degradation, and oxidation, can cause changes in strength, embrittlement, gloss, or any number of combinations of property changes.
Thus, rather than the narrow question “color change or polymer degradation?” a better question to ask oneself might be “What type of failures do my products typically experience in the field?” or “What modes of polymer degradation concern me the most?” The answers to these open-ended questions are more likely to lead to an effective weathering test program