Ring culture in the GH

I noticed something today, that was new to me and made me happy. The compost in the big pots is really warm as was the outside of the pots. Much warmer than the soil in the beds on the other side of the GH. I asked the Duck why and he quacked that black pots :-
Heat up quickly and provide little insulation.
Avoid using in full sun in hot climates with heat-sensitive plants.
OK to use in shady positions or for plants that need soil warmth.
Useful for creating a warm microclimate during cold months as the black colour tends to absorb heat and hold it better than light colours.