if vein are blue, why is blood from a cut red?

Human blood is red.
oxygenated is bright red,
deoxygenate is dark red.
slugs blood is green (funny copper story)
When looking through the skin at something gloomy, it looks blue becuase of a phenomenon that red light scatter more easily and let the blue light get into, therefore blue.
if someone have a deep mole or melanoma, thoughtful to certain layer of the skin, it appears to have a blue tinge.
Because Oxygen react with the iron surrounded by your blood and "Rusts" in a Small course!
The oxygen in the upper air gives the blue bloods its red color.
It's not the vein that are blue, it's the blood running through them. When blood becomes de-oxygenated it looks blue contained by your veins. Once the blood is exposed to oxygen, or runs spinal column through the lungs and gets re-oxygenated, it appears red.
When oxygen comes into contact next to the heamaglobin in the red blood cell the cell takes on a gaping red 'oxygenated' colour due to the cativation of the heamaglobin, when this oxygen is exchanged for carbon dioxide the heaaglobin is inactive and go back to its norma 'deoxygenated' colour a deeper red more purple within shad than hte activated colour. the veigns and arteries themselves are a washed-out yellow cloour, this make the blood look more blue than it actually is, hence when you cut yourself from a veign its a muddy red not blue and when you cut yourself from an atery its red red red. Hope this helps