Page History

Visible

Does the same thing Color

For organization purposes only. Examples are to choose the same color for a layer and all its children or to attribute the color some meaning.

Visible

Same as the layer hide/show icon. See below for more information.

Frozen

Does the same Same thing as the layer freeze/unfreeze icon. See below for more information.

Export Layer Pak 

The layer's resources will be marked for use in the layer switching system for fast streaming. See Layer Streaming.

Default Loaded

This The layer will be loaded by defaultat startup even if it is not visible. See Layer Streaming.

External

When this checkbox is enabled, the layer will be stored as a separate .lyr file on disk, enabling better use of version control systems.
The layer will automatically be exported when your level is saved, and imported on loading.
Un-checking this box will make the layer part of the .cry file again and the external .lyr file will no longer be updated. External layers are indicated by an underlined layer name.

Export to Game

When this checkbox is enabled, the The layer will be exported to the game when you use File -> Export to engine.
Un-check this if you don't do not wish to see export the objects contained in the this layer in to pure game mode. This useful for objects used for development. This option is distinct from the visibility setting in the editor. See also 'Platforms' to export depending on the deployment target.

Brushes Have Physics

Brushes within a layer with this disabled will not have physics. This is good for distance background objects to save on performance.

Platforms

You can choose if you want the layer to only be exported to specific platforms. This is useful to have different assets or logic depending on your deployment target for performance reasons or for exclusivity.