Well I haven't got the opportunity to fly above that level as yet, so may be you are right, the day might look vmc but according to sacaa car part 91 no vfr flights are allowed above fl195. In uk, no vfr flights are allowed above fl200 or aircrafts flying at transonic and supersonic speed.
Now i don't know why this limitation has been set, may be altitude cannot be maintained with reference to horizon only.