I think Option (3)
The arms mostly contains old blue and blue-white stars
Explanation:
Spiral arms are the regions in stars extending from the middle of spiral galaxies and the barred spiral. Those long, thin areas look like a spiral and therefore give their name to spiral galaxies.
Spiral arms, though, include many young, blue stars, that render their arms so bright (due to the high mass density and the fast stellar forming rates).
