Where can you find an easily removable window covering for a high window that brings in a lot of sun during the day but which you want to have open in the evening?

Your best bet is a "roll up blind" and it comes in the type such as venetien blinds and also bamboo. When you don't want the sun in just roll it down (long cord) tacked back against a corner of the wall and roll it back up at night. If you contact a window company there are new windows out now with the blinds inside of the windows that can be opened and shut, but they are fairly expensive.