Now lets say you wish having a slight blue tint on the veins using a rather white skin, do it just like above applying the skin texture to the color node of the Vein layer. Give a slight blue touch, you will not see it by eye as it will almost be like a white with the blue info. Again set your preferred bump strength depending the Vein map you are using.

If you wish having for instance a stronger effect on the chest with decreasing vain bump and a blue touch you can make the color dark blue in direction of black and reduce the values of the HSV from 0.02 to 0.002 really low the bump will need a allot higher value so instead of .007 .17 or more again it all depends on the Vascularity map you created. My map is just a basic and sure can be done allot better. Painting it keep the lines thin you always can enlarge them for your needs, give them a slight zig zag where the branch nodes are make it stronger like little knots, that will give a nice realistic effect.