Henrik....you da man! So simple yet not so obvious. At least for me.
Thank you so much!
Ricardo,
you just need to set the option RegionBoundaryStyle to None:
RegionBoundaryStyle
None
ContourPlot3D[x^3 + y^2 - z^2, {x, y, z} \[Element] Ball[{0, 0, 0}, 3], RegionBoundaryStyle -> None]
