Right, I'm not worried about the sunlight warming the engine. Just the extra coating reducing the heat transfer effectiveness of the cooling fins and case by adding a small layer of insulation. Metal is a great heat conductor, paint isn't. An example of this effect is with exhaust pipes, if you give the inside of the pipe a good coating of high temp paint it will prevent it from bluing up.
edit: Black is a great for getting heat from sunlight. Is is because all color we see is reflected light. White reflects nearly all colors of light wavelengths, thus it stays cooler is sunlight. A blue object will absorb all the wavelengths but only the blue wavelengths, so it reflects blue and that's what what our eyes see. A black object will absorb the broadest range of the light spectrum reflecting little back, so it becomes warmer and retains more of the light radiant energy. I don't believe the color of the paint will effect how well it absorbs or dissipates engine heat significantly. Color only plays in role when the paint or object is heated by a light source.