Why do walnuts turn red? Give me a scientific explanation.

Related to the reflection and refraction of light.

1, walnut shell is wooden, light in color and has many small holes on its surface. When the light shines, a lot of light will be directly reflected back, so it looks like the true color of wood;

2. Because there are oil stains and dust on the hands, after playing for a long time, these oil stains and dust gradually penetrate into the gaps in the wood of walnut shells and finally fill these gaps.

When the light shines again, on the one hand, magazines such as dust fall into the gap, making the color darker; On the other hand, because the oil is translucent, it fills the gaps and forms a lens, which makes the walnut shell crystal clear and beautiful as jade.