From Cedric Pinson, The following modification are

Update Timeline.cpp to add current layer to the ActionVisitor, use correctly the priority
Add accessors in Action.cpp to retrieve protected data
Split files and rename them to classname
Change de default color of UpdateMaterial to FFOOFF to detect unset value
Add accessors in LinkVisitor instead of accessing data directly
Update osganimationtimeline example to fit the api callback

src/osgAnimation/UpdateCallback.cpp

@@ -130,7 +130,7 @@ UpdateMaterial::UpdateMaterial(const UpdateMaterial& apc,const osg::CopyOp& copy
 UpdateMaterial::UpdateMaterial(const std::string& name):
     AnimationUpdateCallback<osg::StateAttribute::Callback>(name)
 {
-    _diffuse = new osgAnimation::Vec4Target(osg::Vec4(1,1,1,1));
+    _diffuse = new osgAnimation::Vec4Target(osg::Vec4(1,0,1,1));
 }
 
 /** Callback method called by the NodeVisitor when visiting a node.*/