Why blood is red in color but not veins?

If blood is red , Why our veins are blue?

Our blood is always red in color whether it is pulsing from our veins or gushing from our wounds. Veins appear blue because they are lying under the skin. Skin scatters more blue light than red. Skin around the vein looks more red than vein itself. So, the color contrast enhances the vein to look blue color. Human blood is always red because of the presence of iron content in it. The iron mixes with oxygen in our lungs and forms red color. But the blood of all other animals is different beacause not all blood have same chemical makeup. Spider blood has more copper than iron. Hence, the copper in their blood mix with oxygen and forms blue color. By contrast leech blood has oxygen but less concentrated than the human blood, hence it is green in color.