Files linked between them

Suppose you have a file called logo.ai. Use File  >> Place >> CHECK LINK to place logo.ai into all your banners, flyers, etc. By Linking instead of embedding, they will reference the logo.ai file.

Before you do that I would recommend thinking about your bounding box. Might the physical size change during revisions?  If so add a bounding box filled with none that is large than your art. In this example I added a rectangle filled and stroke with none. This way if the lowercse g could be made to dip down lower or any other cahenge. As long as it does not go outside the bounding box, the logo will be in place in all my designs. 

To an extent, you can achieve this by placing files into other files (such as you would do with a logo.

You can also use CC library items.

What will not work, is change a color and then wait for it to happen in other files as well.

If this is about designs to be used online (banners, social media etc.) take a look at Adobe Express.