I am 5'6" and 140 pounds and these pants fit pretty well in medium. Slightly baggier fit for my size but it is still a little slim and kinda tight around the boot. Not a ridiculous amount of bunching but I definitely have some room. If you are a similar size to me and you want a really super skinny look then go for the small. They are made from a material that looks like regular pants but it is still super water proof. Comfortable too and seems to be of good quality.
As for the color, the moss isn't as light as the picture shows. It is slightly darker and a bit more tan whereas some of the pics make them look almost stone/light greyish colored. And they also have a green hue when in certain lights but for the most part are khaki.
Nice pants overall.