PATHOLOGY

Detailed explanation-1: -People whose blood is low in oxygen tend to have a bluish color to their skin. This condition is called cyanosis. Depending on the cause, cyanosis may develop suddenly, along with shortness of breath and other symptoms. Cyanosis that is caused by long-term heart or lung problems may develop slowly.

Detailed explanation-2: -Superficial veins are the type that you can see. They may look green instead of red because the color green has a shorter wavelength than the color red. They may also look blue or blueish-green because blue also has a shorter wavelength than red.