This is what I took away from the video:

Bigger difference when no air is flowing through the cooler,

Minimal difference when air is flowing through the cooler.

While it will lose heat quicker when painted black with no air flow, it also works the other way and soaks heat quicker, so I suspect that with a top mount setup, this will work against you as your cooler sits in a hot engine bay. Sitting at the lights, or waiting to launch at the drags, the heat soak inwards will ruin it all.