The radiators on the ISS are a high-emissivity white paint, meaning that they are dark in the infrared spectrum where the heat is emitted.  They are white in the visible spectrum to reflect sunlight.

The radiators on the shuttle are have a two-layer coating: a silver reflective layer covered by a thin Teflon film.  The Teflon layer is opaque to infrared light, so the high emissivity of Teflon dominates.  Visible light passes through the Teflon layer and is reflected by the silver layer, so the solar absorbance is low.

The radiators on the Shuttle are exposed to more direct sunlight (the radiators on the ISS pivot so they are typically close to edge-on to the Sun), which is why they use the higher-performance but more expensive dual-layer design.