This is one of over 4598 effects generated by Filter Forge, a Photoshop plugin that allows you to create your own filters.
To open this filter, you must have Filter Forge 2.0 or higher installed on your computer. If you don't have it installed yet, click here to download Filter Forge
When you apply stain to an object or image and wipe it back off, parts appear dark and where more stain was removed there will be lighter areas. This is a way to add color in only some areas of an image. Also part of this filter is an outline overlay effect. The ability to change the color of both the stain and the outline makes for some unusual image effects.
Stain, outline, image effect, color overlay