Final answer:
Postmodernism in architecture, exemplified by Michael Graves' work, features the rejection of historical references, playful ornamentation, and the retention of functionalism.
Step-by-step explanation:
Postmodernism in architecture, as exemplified by the work of Michael Graves, is characterized by several key features. One characteristic is the rejection of historical references, as postmodern architects incorporated or appropriated styles and ornaments from the past. Another characteristic is the utilization of playful ornamentation, where buildings were decorated with colorful and whimsical elements. Finally, postmodern architecture still focused on functionalism, retaining the functionalist core of modernist buildings but adding decorative elements.