Browning means death. This could either be time related; foliage dies off after a couple of years, these trees grow from the tips of their branches outwards, so naturally, the closer to the trunk the foliage is, the bigger the chance it'll be old. But it can also be related to the health of your plant. If the sap flow stops, it turns brown because it's not getting water in there and the part has died.
Brown parts are usually drained by the tree for nutrients. It's a more or less natural recovery process. The dullish grey-green described below means sudden death, more unnatural.
If it's a purple-ish shade, that indicates stress; sap flow is restricted AND/OR the nights are still cold.
Some junipers get a golden tone in winter, this doesn't mean anything except that they're not purple like the others. They perk right up in spring. Sometimes it can be hard to distinguish the golden tone from the brown one, but the crispyness of the foliage tells a lot. If it's dead, it's crispy. If it's alive, then it feels like regular foliage. If it's dying, it'll feel floppy like old lettuce.
A dull greyish green color indicates that it's dying and there's no connection to live tissue whatsoever. This happens when a plant just gives up (indoor junipers for instance) and stop living as a whole. Of when a branch has been twisted and turned until it lost all connection to living tissue (see the second picture of your post, it looks like there is a snap in the righthand loop but the connection to the trunk might also be damaged).
If you wait long enough though, the grey stuff will eventually brown up due to natural breakdown.
I've seen grey foliage perk up, but only once or twice out of a hundred times.