Watercolour triangles let students paint paper with watercolors, wet on wet, similar colors. Let dry and cut into triangles. Students pick triangles and glue down randomly, leaving white around each one. Maybe try with black or other color background?
Everyone gets a square with a quarter circle, this is the end result- could be a good ice breaker beginning of year activity. Each student decorates the square and includes their name. Nice way to decorate the bulletin boards in the beginning of the year!