The carapace of Muhlenberg's turtle is light brown to mahogany to black with a lighter center or, often, a yellowish or reddish sunburst pattern on each scute. A low dorsal keel is present.
Bog turtles are flat at hatching, and become more domed with age.
The plastron is brown to black with small areas of a lighter hue. The bog turtle's trademark is a large patch of orange, red or yellow on the temporal region of the head often extending onto the neck, as shown in the photograph. Occasionally, the patch is split into two parts. The dark limbs are usually suffused with red, orange, or yellow mottlings. Male bog turtles have a larger head, a longer, thicker tail with a more posterior vent, longer front claws, and a wider and less high shell than females.