leenia, if you used a black cloth in Oz the way you described, the heat inside the car would rapidly become intolerable. Even in Tasmania, the part of settled Oz furthest away from the equator. I recall a fiddle player who left his fiddle in its (black) case on the parcel shelf (under the rear window) of his sedan for a while. When he later opened the case he found he had a complete fiddle kit; all he had to do was assemble the parts.

In Oz, we spread highly reflective screens, inside the windscreen across the full width of the car, to reduce heat entry into the car.

Cheers, Rowan