There's a few products out for greenhouses that are a "shade paint." They are a white paint that is temporary and easy to wash off.
I have a poly sheeting, aka "greenhouse plastic," over my greenhouse, because it is so much cheaper than the polycarb panels. I tried to make my own shade paint from diluted latex paint, but I couldn't wash it off the following year, even with a pressure washer.
So I use mud. It works just as well...until the rain washes it off. I only need the shade for a few weeks anyway, towards the end of the season. Plus, I get to have the fun of throwing buckets of mud. It feels like vandalism
