[Just thinking (OP)]

saturn v moon rocket.PNG (475.39 kB . 781x740 - viewed 1026 times)Does anyone know why the Saturn v and many other rockets but not all have the black markings on their surface?

[Halc]

The things are mostly white (especially in the areas directly against fuel tank) to help keep it cool.
The black blocks (mostly between stages where there wasn't fuel) were painted on to help with tracking from the ground. It is much easier for instance to notice roll of the rocket with the alternating stripes or checkers.

[Just thinking (OP)]

It is much easier for instance to notice roll of the rocket with the alternating stripes or checkers.

That is the perfect answer. Also but never used the ground crew visual teem could tell if there was a problem that might require the crew to eject or abort the mission by activating the escape tower in the first two minutes of the launch.