Skinning is the process of changing the appearance of a component by modifying or replacing its visual elements. These elements can be made up of bitmap images or SWF files (Graphical Skinning), or they can be class files that contain drawing methods that define vector images (Programmatic Skinning).
Embed images in the Flex application (GIF, JPEG, PNG or SWF files containing symbols).
Extends one of the existing skin classes.
Implement the required interfaces and write the rest yourself.
You can create a UIComponent that implements the required interface. Which interface you implement depends upon what you are trying to create. (ie Does it need a border? Does it need to reflect states?)
You can implement:
Ensures that any implementing class has an accessible name property, which is used to determine the state of the skin.
Ensures interface ensures that any implementing class has an accessible borderMetrics property.