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.
Golden-crowned Snake. The Golden-crowned Snake is brown to grey above and pink below, with a yellowish crown-shaped marking on the head which gives it its name. related species is the Dwarf Crowned Snake, Cacophis krefftii, which is much smaller (25 cm), with a dark-grey to black body and a cream to yellow hood over the nape of its neck. This species ranges from the central coast of New South Wales to south-eastern Queensland, and does not occur in Sydney.