In this article. Varicose veins are large, raised, swollen blood vessels that twist and turn. They usually develop in the legs and can be seen through the skin. Spider veins are smaller, red, purple, and blue vessels that also twist and turn. Spider veins are easily visible through the skin, as well.They are typically visible on the legs and face.hey usually develop in the legs and can be seen through the skin. Spider veins are smaller, red, purple, and blue vessels that also twist and turn. Spider veins are easily visible through the skin, as well. They are typically visible on the legs and face.