In theory, a light-color piece will not let heat through (will reflect the heat), whereas a dark-color piece will let heat through.
That is why "old style" copper radiator are painted black, they let the heat (from the coolant) out better. Lighter colour (shiny stainless steel, for instance) headers do help in keeping the engine compartment a bit cooler.
What amazes me (and is way beyond my comprehension!) is that the color does not have to be on the same side a s the heat to affect its transmission, ie on a rad, the black color is not on the side of the heat, but it does help the heat transfer.
That theory works with any kind of paint, the "VHT" only means the paint will withstand the heat without burning/peeling off. So, if you are painting the roof of your car to keep the inside cooler (yes, it really works!), you do not VHT temp.
So, the simple answer to your question is: yes, it does block some heat. Probably less than real ceramic coating, but might still help.