Question

Even though the hubble law for galactic motions indicates that the spectra of all galaxies should show redshift as a consequence of the general expansion of the universe, the andromeda galaxy m31 appears to show a blueshift in its spectrum. why is this?

Answer 1

This is because Andromeda is headed toward the Milky Way. Eventually it will collide with our galaxy. When something is moving toward you it's light appears blue or, or blueshifted.