I only started making gravy a year or two ago, so I don't fully understand the process, although I appreciate the taste. As I was making gravy for Thanksgiving, I noticed that the color was significantly yellow and it wasn't clear, but milky-opaque. I know from this question that the yellow color is from using the fat I skimmed off of my stock to make the roux. (I made a combined chicken and turkey stock.)
But what makes the gravy appear opaque and almost milky? The color came almost as soon as I mixed my stock into my roux.
(Incidentally, my stock wasn't hot when I added it to the roux. Would that make a difference?)