Prestone and others also sell a flush kit, where you install a "T" in the heater hose to which you hook up a garden hose to flush it out. If you want green coolant, you may want to consider the "all makes/all models" antifreeze. Prestone and others make that, also. It has a green color, and is compatible with Dex.
As Bill said, you have to be certain to remove ALL of the Dex before going back to the old green stuff, which is quite time consuming. Either of these options take care of that problem.