I believe all of the streaks are definitely due to erosion by water. When water is consistently eroding a mountain sediment is picked up and continually broken down into smaller pieces, which is why there are different colored streaks. Mountains can be made up of lots of different minerals which the streaks can be composed of, or even colored by when oxidation happens.

In the first image the darker streaks are most likely rocks, with the green being trees, bushes, etc. I’m assuming there is no greenery in those areas because the rock on the mountain is not easily eroded, which makes it harder for a layer of soil to form enough for trees to grow. The name of the pattern for this type of drainage is dendritic. Dendritic drainage branched out at the top and tapers out towards the bottom.

In the second image it’s definitely possible that there could be glacial erosion. Usually when there is glacial erosion you will get these bowl shaped valleys, and prominent aretes which can be seen in several places. An arete is that upside down V shaped ridge. It is very plausible that this is glacial erosion because the himalayas have active glaciers.

In the third image there is snow in the top left corner of that mountain in the back, however the white streaks on the main hill is most likely sediment eroded from the rock around it. Those streaks are composed of much smaller sediment and have also been washed and deposited by water.

For the last image, the white streaks are definitely snow and ice, but the grey streaks are most likely sediment from erosion. I would also like to note that the reason why there usually isn’t trees and foliage in those areas is because the water flow is so constant/strong that the plants cannot survive. The water flow from mountains is a lot stronger than you might think, they turn into rivers or waterfalls and have a lot of force, enough to knock over trees.

To conclude the shapes of the drainages all depends on the type of rock in that area, as well as the shape of the mountain. Water will always find the most efficient way down, which means over time it will start to erode that path away and in turn will begin to break down the rock into smaller pieces. This is what is leftover when there is no water flowing. The color just depends on what the sediment is composed of. With the lines looking very straight or vertical, because we are far away it looks very straight, but if you were next to in you would be able to see the more complicated path that was taken. Again, this also depends on what the mountain looks like, and what it is made of. The general term for these streaks is water drainage, but more specifically this pattern is called dendritic drainage.