You'll notice that the places that you see blue veins are in areas where the skin is thin and the blood vessel underneath is pushing up on it stretching the skin over it. Light hitting the dark color of the vein underneath the skin, in combination with the skin itself is what causes it to appear blue in these areas.
Common krait. The common krait (Bungarus caeruleus), also known as Indian krait or blue krait) is a species of venomous snake of the genus Bungarus found in the jungles of the Indian subcontinent. It is a member of the big four species, inflicting the most snakebites on humans in India.
The word reticulated means net-like and refers to the beautiful network pattern on these big Southeast Asian snakes. They are often killed for their skins when found in the wild. Please be aware that the reticulated python is not a snake for beginning snake owners. Reaching lengths up to 33 feet, the longest snake on record was a reticulated python. By the time they are two years old they can be over eight feet long and weigh fifty pounds. This is large enough to kill a human.