In what climate is hot or cold, venous blood will be lighter and why?

By itself, venous blood is quite thick and dark in comparison with arterial blood. This is due to the lack of oxygen in the venous blood. In a hot, dry climate, the human body is more saturated with oxygen, the blood in the veins is somewhat thinned, it becomes more like arterial. At the same time, a cold climate, on the contrary, stimulates the thickening of blood plasma. That is why in a hot, dry climate, venous blood will be lighter than in cold weather.