I had an old can (steel can) quart size of DOT3, it was kinda yellowish and a little thick. Viscous may be the right term. I had bought a new quart size plastic bottle and it is nearly colorless and less viscous. When I rebuilt the MC and caliper, I used the new stuff and poured out the old stuff, but saved the can. Don't know why, I suppose because I've had it for 20 years.
Spose the old stuff had some water in it? It was not milky looking, just a little yellow.