The above image shows a blue-colored warrior character. His armor legs, arms, helmet, and weapon are all blue. Let’s say you want to change his color to green. By using a document color on every part you can change the color from the swatches palette and instantly have a different character.
Use Symbols. Often you will have many duplicate objects placed around your canvas, such as level tiles or bricks. But what if you want to change all of the duplicated objects? You can use Symbols. Create one object and turn it into a Symbol. Then duplicate it. Whenever we change something in one of the Symbols, the others will change too.
Organize with the Assets panel. Place all of your objects in this panel, and you’ll get an overview of all the things in the game in one place. You can group them by any criteria you want: the level that the object is used on, type, color, etc. Then you can drag and drop these objects to any document you have open. You can check for visual consistency, scale, how they appear in another level, and so on. You can also make mockup screens or “screenshots” of your game.
Furthermore, you can store UI elements in the Assets panel like button designs, switches, and icons, and use them when designing your game’s interface.
Source: Unity Technologies Blog