Blue represents space, like the sky or the space in front of you. The space of the sky is limitless. The atmosphere surrounding the Earth with oxygen and carbon dioxide in it has to do with the element of air (in all the complexities of air) than to do with space. The space is filled with air and birds and scents and pollution and wonder, but space is not air. This distinction is significant because blue: space is signalling the space in your room to be the same as in a universe, within an atom, between two thoughts, or outside your window. Space is uncompromised regardless of what occupies the space.
HUM is a enunciation of the force of wholeness. It scatters the disparate in order to wipe clear a space, like blowing dust from a mirror. HUM paves the way for the new, but not because the new is better per se. Rather, the new is a fresh attempt at wholeness, or letting be what IS.