I suggest you don't use black cream. It will be messy. But you can remove excess cream by simply rubbing with neutral wax.
The shoe will darken in time. Just do your normal regime, but it will take time.
You can burnish the toes and the heels/hind quarters with black/dark brown wax. Just apply wax thin layer by thin layer.
If you wish to darken the rest of the shoe, then use alternate layers of burgundy cream, mid brown and dark brown cream. Layers must be very thin.