How to read the thermal charts

[Christer Dahl 2]

I cant figure it out.
Color indicates altitude, but if its grey, does it mean thermals are on ground level? I assume not, but could anyone please explain it a little better?
Cheers

[idefix37]

@christer-dahl-2
Thermals are upward currents of air due to convection.
When Windy shows a grey colour, that just means there are no thermals, the atmosphere is stable.

https://en.m.wikipedia.org/wiki/Thermal