Why do plants shade with black cloth? Wouldn't black absorb all the light in theory?

Doesn't black theoretically absorb all the light? Yes, that's right. That's the effect.

The black cloth absorbs all the light, so the light can't be transmitted, so it can't shine on the plants, thus achieving the effect of shading.

It is the black cloth itself that absorbs light, so plants can't absorb it.