Blood is never blue. It’s always a shade of red. The only reason it appears blue in veins is because veins tend to be closer to the surface of the skin and blue wavelengths of light are the only ones that can penetrate to that depth. As for the arteries…you typically can’t see them because they’re too deep.

Note: with regards to the picture – in textbooks the veins are colored blue to differentiate them from the arteries.