The material that changes its color depending on how you look at it is called a dichromatic material. Dichromatic materials have two distinct colors that appear to change when viewed from different angles. This effect is caused by the way the material reflects light. When light hits a dichromatic material, some of the light is absorbed and some is reflected. The color of the reflected light depends on the angle at which it hits the material.

One example of a dichromatic material is alexandrite. Alexandrite is a type of chrysoberyl that changes color from green to red depending on the type of light it is exposed to. In natural light, alexandrite appears green, but in artificial light, it appears red. This is because alexandrite absorbs blue light and reflects green light in natural light, but it absorbs red light and reflects green light in artificial light.

Another example of a dichromatic material is iolite. Iolite is a type of cordierite that changes color from blue to violet depending on the angle at which it is viewed. This is because iolite absorbs yellow light and reflects blue light when viewed from one angle, but it absorbs blue light and reflects violet light when viewed from another angle.

Dichromatic materials are used in a variety of applications, including jewelry, art, and optical filters.