The human eye senses color mainly through three primary colors – red, green, and blue. That is why in television signals these three colors are used for producing the color pictures. The blue component of the scattered light is almost ten times stronger than the red. Even though the violet and indigo are scattered more than blue the eye senses mainly blue. Therefore when we look at the sky away from the sun the sky appears blue.
The "wavelength" of light is what you may be referring. The wavelength of blue is much shorter than red, hence the blue wavelengths are absorbed by gas molecules in the air and are scattered more frequently, while the red spectrum is not absorbed as frequently and passes through.