Outline Image Effect for Unity
Sprite/Line/Mesh renderer support
HDR support (useful for bloom, etc...)
Alpha cutout option
Additive outline rendering option
Merged outline between renderers (or you can add outlines between different colors)
Erase option to keep outlines behind specific renderers
Per renderer color support (up to three different colors)
Download the files and open the project OR place the "Assets/OutlineEffect" folder in your Assets folder
Add "Outline Effect" component to camera
Add "Outline" component to renderers