Coffee brews clear or cloudy, usually depending on the filtration. Paper filters will normally brew clear, where's metal filters allow a degree of soluble solids to pass into the brew, which is more opaque.
But here's an open question: why does coffee that brews fairly translucent become opaque as it cools? Do you have an explanation? Why is paper-filter brewed coffee less transparent as it cools?
The coffee in this little video is that same in both cups but one was cooled to about 95f and the other is about 128 or so. Can you see the difference?