Hello! The blue vein in your arm is a vein. Your arm is more obvious when it droops, and the longer it droops, the more obvious it becomes. This is normal, because blood and water are the same, both flowing downwards, and venous blood is the blood that returns to the heart. The arm is drooping, and venous blood returns slowly. There is siltation, so it will bleed. You said the veins stood out.

Suggestion: What you said above is a normal phenomenon, not a disease, and no treatment is needed.