Why are the veins blue?

Our blood is red. Venous blood is slightly darker than arterial, but that has nothing to do with it. The veins are also red. But we see blue veins for physical reasons. They are located under the skin. Because of this, a discoloration of the veins on the surface occurs. It can be compared to mixing paints. If we mix two paints of different colors, then we get a new shade or color. Also, the red spectrum of the rays is absorbed, but this is a more complex explanation, which is based on the optical laws of physics.