According to multiple sources, the heat shield on JWST is expected to exceed 85 °C. The average temperature of the earth is only 15 °C, so this is about 70 °C higher at roughly the same distance from the sun. I assume the reason is that successive layers of the heat shield reflect heat back towards Layer 1, rather than allowing it to diffuse through the whole spacecraft, in addition to the heat generated by active components on the spacecraft itself.
That is to say, I assume that the 85 °C temperature cited reflects the fact that the sun side is a combination of energy collector, energy reflector, and thermal radiator (although I recognize that the shield is also designed to dump heat out the sides as well). However, none of the sources I have looked at says that is actually the case. Can anyone confirm this theory or give a correct explanation?