Digital photographs of ice and food colouring on bath
Always one to take a theme literally (if it is going to be cheap and easy enough), I froze a sheet of ice with food colouring outside overnight (it being February at the time). It was not cold enough to actually freeze the food colouring, but enough clung to the ice to provide a bit of contrast. I also did a sort of ice version of a green man during the video call (below).
Pencils on paper