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I found this article while hunting for heat shielding for the part of the wiring harness that goes to the starter (the OEM shielding is ragged and several of the wires are cooked). It deals with airplane engines but it was pretty interesting none the less.
If you don't want to read it here is what I got from it.
Painting an engine increases radiant cooling but the color of the paint doesn't matter.
Paint the engine compartment black to absorb radiant heat.
Components that you want to reflect engine heat and that radiate their own heat should be painted white.
Components that you want to keep cool but don't radiate their own heat should be reflective metal pigmented paint or CHROME :)