No students were allowed to see the final image until all of the squares were finished.
Though we started with a fairly good variety of color in our available tissue paper supply, many students had a hard time noticing the subtlety of colors present in a particular square. They would notice, for example, that their square had purple spots, but not that those purple spots were a very pale shade of lavender. Adding dark purple tissue paper where light lavender should be causes some problems in the final piece.
Throughout the process, the students tried to guess what the final piece could possibly be. Some of them tried to guess famous pieces of art or famous artists.
I told one student, "It's not something you've seen before, it's just a pointillist piece of art."