Why are my veins sometimes very dark so i can see most of them? they don't stick up they justare darker and more eaasily seen

Dark veins: Firstly veins carry deoxygenated blood so they are naturally darker. Secondly if they are closer to the skin like most are and you have light skin they will be more obvious.

Veins carry low oxyg: Veins carry back to the heart your nonoxygenated blood arteries carry oxygenated blood from your heart and veins return it when de oxygenated its dark as opposed to bright red when oxygenated.

Normal.: The prominence of veins through the skin is affected by many factors including levels of hydration and dehydration, body temperature as well as outside temperature, medications and even levels of stress. Fair skinned people tend to have more easily visible veins than darker individuals and hereditary plays a strong role also. In a healthy person, visible veins are usually not of any concern.