If netatmo station detectes less than 0°C, then the wallpaper will change in primary yellow
If
Temperature drops below
This Trigger fires every time the temperature drops below a value you specify.
Then
Update device wallpaper
This Action will update the wallpaper on your Android device from the image URL you specify.
ID T96fRjgN
Explore more great ways to automate Android Device and Netatmo Weather Station