Deoxygenated blood does have a different shade to it than the deep scarlet red of oxygenated blood - it's hardly noticable though, but not wrong. This is because of the way the oxygen binds to the heamoglobin, the extra ligand (I can't remember the exact chemistry) alters the energy levels so when electrons in the bonds get excited they emit a different amount of photons - which is like energy &amp; it's in the visible light wavelength - thus the extra bonds alter this wavelength (COLOURS N SHIT YAY!) making it a slightly different colour to deoxygenated blood (more redder/ no blueish hue) That's not an exact explanation, I haven't studied this in a while, I'm sure someone will correct me