VFR
Of course you can fly VFR on top even when out of sight of the surface, unless your particular licence held precludes so such as the UK issued PPL! Even the UK issued PPL holder may may fly VFR on top should they be able, at all times, to maintain some sight of the surface.
You may fly VFR at all times that it is VMC (within Class A airspace - SVFR) and when in addition the VFR vertical and horizontal distances, that are prescribed, are maintained from cloud.