Instead of composing an image, the New York artist Ellsworth Kelly believed in “choosing things out there in the world and presenting them.” He took shapes from the world and simplified them, a strategy that gave rise to his mesmerizing color fields. While Kelly’s large-scale paintings and sculptures are familiar to most, his experimentation with postcards has seldom been explored. Between 1945 and 2005, he created over 400 postcards, using them as preparation for larger works. In Saratoga Springs, 150 postcard collages are on view, some of them from places to which Kelly traveled—Old Chatham, Paris, New York. —E.C.