The mouse found out: The “walls” (i.e. the outer skin) of the veins are not blue. Yet veins look blue even though the blood is red. To understand this, the mouse looked at how we see colors.
Simply put, all colors are contained in sunlight. If the light hits an apple, for example, the rays of light are either thrown back, i.e. reflected or absorbed – the technical term is “absorbed”. A red apple reflects the colors in such a way that our eyes see “red”. The other colors are swallowed.
Now we come to our skin. The light penetrates our skin at different depths.
The blue light is reflected faster. From the veins. The red light, on the other hand, penetrates deeper and is swallowed up there. This is why veins look blue.
The paler the skin, the bluer the veins look. That’s why the noble people used to say of themselves “We have ‘blue blood’.” They were less outside and therefore rather pale – you could see the blue veins particularly well.
Only veins that are very close to the surface of the skin, such as on the face, are different. The red part of the light is not swallowed, but reflected – that’s why we turn red when we’re excited and not blue.
