My answer on Quora to “Who should create Oracle ADF skins: Developers or designers”
If you are on the latest ADF version (12.2.1.x.x), you have access to the web-based Theme Editor. In this case, your designer should use this user-friendly tool to create the skin. It has some limitations, but the designer is best placed to work around these.
In earlier ADF versions, a CSS developer is needed to develop the skin, and the designer just produces a graphic in photoshop or similar. If you don’t have a specialized CSS developer, somebody will have to learn CSS, because ADF skinning uses all normal and some uncommon CSS features.