Black absorbs energy from light in the form of heat. Black, so far as I'm aware, doesn't dissipate thermal energy in the form of light. I'm fairly confident I would have noticed a phenomenon like this with IR optics or NVGs in my military career if this were the case. Thus, I'm confident enough that there is no truth to this.
Additionally, white paint may reflect light, and thus it may reflect infrared light, or radiant heat, as well. I'm not sure how much radiant heat is actually transferred from the block to the lower intake, but I suppose there is some possibility of effectiveness. I doubt it's significant, and highly doubt radiant heat outweighs the heat of conduction or convection. However, I suppose that even a coat a paint provides a slight thermal barrier from these forms of heat transfer, too.
Chris