That is the color of the lens coating, whose scientific name is antireflection coating.
When the thickness of the coating is 1/4 of the red wavelength, the reflection of the coating will be blue. However, the coating itself is colorless, so the color of the coating will not change (accurately) It is said that there are minor changes).
Coating is an important process in modern optics, and the quality of the coating directly affects the imaging quality.
For example, the famous Zeiss T* (usually more commonly seen on Sony cameras) is a coating process with a patented technology. Only lenses using this coating process can be called T. Just tear off the camera module.