Ahh okay. It makes much more sense to me as I read it more. But just to clarify on distance, larger distances would make the magic less opaque versus short, and solid objects containing no magic, such as brick wall, would impose the "clear vacuum" and could contain the magic from being detected by his sense based on the concentration of said magic? With that cleared up, I can put the nail in the coffin of my understanding of your proposal. 

Although I do think your explanation makes the ability easier to justify, explain, and apply rather than color-coding all of magic to the previous blue-green and then attaching it to his hearing. 
I would still like the souls and spirits of "living" things to have color however.