Heat dissipating materials for a wall that gets very hot?
Since it's a "Heat in summer" problem, a traditional decorative and edible approach would be to train/trellis a plant or plants in front of the wall - grapes, vining tomatoes, espaliered fruit trees, perhaps even a fig depending on your climate - or purely decorative things like climbing roses, wisteria, or ivy - but ivy can be surprisingly aggressive, so research carefully.

This can be especially useful to grow things that might be a bit marginal in your climate and could stand some more warmth.