Conclusion
The vein that you can see through your skin is called the superficial veins. These veins appear to be either green or blue instead of red because green has a shorter wavelength than red. The color of your veins which appears to be green or bluish-colored is more visible if your skin is a lighter color.
References;
[1] https://www.verywellhealth.com/what-are-capillaries-2249069
[2] https://www.britannica.com/science/artery
[3] https://www.mayoclinic.org/diseases-conditions/muscle-cramp/symptoms-causes/syc-20350820
[4] https://www.nhs.uk/conditions/varicose-veins/
[5] https://kidshealth.org/en/parents/intravenous-line.html
[6] https://www.healthline.com/health/deep-venous-thrombosis