While Uranus may have the coldest spot for a planet, the temperature overall is warmer than Neptune. It's quite interesting to find such cold spot(s) on Uranus, and it's not understood yet how this could be, apparently.
The logic that a major impact helped cool Uranus is hard for me to accept. Did the Earth become cooler than normal after the Theia impact? Impacts generate heat. The Sun could burn for millions of years just due to the infalling of gas. In fact, the Sun reaches fusion temperatures for that reason.
It was surprising for me to learn just how important opacity is to heat transfer. A star's opacity, for instance, determines its luminosity, and its luminosity determines the fusion rate. Most don't realize that it's not the fusion rate that determines the luminosity, even though the energy comes from fusion. A house heater doesn't control how much heat is produced because the thermostat controls it and that works off the amount of heat that goes out of the house.
Perhaps there are atmospheric conditions that allow lower opacity zones.
It's cool to see Saturn have very blue regions for its atmosphere. This happens when these regions become more clear and light scatters as it does in our sky - our blue sky.