While I was using grass assets for environmental work, I tried to use a brown texture colors for some and leave the others green. However, when I did, it automatically changed all grass even in other collections so all become brown. I want to give them different colors, can anyone help me to fix it?
I can only assume that the grass assets are using the same material. Since the material is shared, edits to material will affect all of them. The solution is to create a duplicate of the material, modify it however you want, and then apply it to the assets that should have the same look.
Let's say you selected one grass patch, in the material properties, you will find a number next to the material name (marked red in the screenshot below) that expresses the number of assets that are sharing this material. You need to click that number to make a copy of that material. Also, give it a good name that you'll remember.
Now, you can freely edit this material as it will only affect the active object. If you find other objects that you want them to use this new material, you can simply assign the new material to them using the dropdown on left (marked blue in the same screenshot).
There is an easy way to make the selected objects receive the materials of the active object which is by pressing Ctrl+L and selecting Link Materials.