Depends on how you want to do it.
A sculpt deformer will make an indentation in the object that is the size of a control sphere, which is created when you make the deformer. You can resize or move around that control sphere, or do something like parent it to your spherical object.
To make a sculpt deformer you just pick "Create Sculpt Deformer" off the Deform menu in the Animation menu set HOWEVER your deformed object MUST have enough resolution to bend around the sphere. Kicking up the number of U and V divisions in the history node will get you there with a simple object like a plane... for a more complex object you may have to model again.
A bend deformer will let you bend the deformed object in one axis. This yields a different effect, but might be more like what you want. Again, making the deformer creates a control object that you have to manipulate to get the deformation.
The purple color just indicates that the shape is being driven by an expression or a deformer.
-- Mark