This restriction is definatly due to temperature issues (glass
transition temperature) with room temperature cure epoxy. This issue
is very real. I can show you damage on the wing of 8A where a
previous owner left a dark object. As for colored markings -
reference TN 278-4 But you will need to read German.

There has been considerable testing by the aircraft industry on this
subject.

H.L.C.
Test Engineer Beech / Raytheon Aircraft, NIAR