Stars in those regions are intrinsically redder in color due to their age and intrinsic composition.
None of the mechanisms here can result in such spectral alteration.
The color of the starlight is altered by reflection from the reddish interstellar dust particles.
Starlight passes through red-colored gas clouds in certain regions, which can add more red light to the stellar spectra.
The interstellar medium is more opaque to short-wavelength radiation than to radiation of longer wavelengths.