What specific optical effect, which requires a medium like skin, is eliminated in a vacuum, causing the blue vein illusion to disappear?

Answer

Diffuse reflection

The scattering phenomenon that creates the blue illusion depends on the presence of tissue layers; when this interference is removed in a vacuum, the component known as diffuse reflection vanishes.

What specific optical effect, which requires a medium like skin, is eliminated in a vacuum, causing the blue vein illusion to disappear?

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