Though this subject has been beaten to death on many sites, I'll say what I was taught "in school" about the colors used.
We all know, black "retains" heat. This is the reason Grumpy, Smokey and a whole lot of other pro engine builders ALWAYS painted blocks and iron heads black. The ratioinale being, the "heat" is INSIDE the block. Painting the outside can draw some of it to the paint, and disapate it to the air. They also did NOT paint the inside of the engines for the same reason. Some of the heat can find it's way "out" through the porous metal. Smokey didn't even like polishing valleys or crankcases for this reason.
The opposite is also true. If the block is painted white or silver, much of the heat is reflected back into the engine.
For the most part, this is all "fluff and buff" in that it really doesn't have a BIG impact on overall performance. I must say, though, 20 degrees difference in oil temp COULD be significant if it's anywhere near "borderline".