Why Does the Central Bulge of a Spiral Galaxy Appear

Why does the central bulge of a spiral galaxy appear red when compared to the color of the spiral arms?

A) UV light from the very hot stars in the bulge has excited hydrogen gas,which is emitting the red Balmer H_ light as a consequence.
B) There is no star formation there,and the star population is dominated by old,long-lived,low-mass red stars.
C) The light from the stars in this region is not Doppler-shifted by galactic rotation,in contrast to that from spiral arm stars.
D) Dust surrounding the bulge has preferentially scattered the blue light from the bulge stars.