Dendropsophus leali Plain-colored Treefrog
Some other names for this species:
San Carlos Treefrog
This species was placed in the large genus Hyla until a major revision of that genus in 2005.
Madre Selva Biological Station, Loreto, PeruJanuary 15, 2013
Plain-colored Treefrog (Dendropsophus leali)
This drab little treefrog is primarily identified by process of elimination; it doesn't have any of the interesting features of other treefrogs. Also, it has that lone white spot on its upper lip.

Here is a complete list of the herps I saw in the wild on my 2013 MT Amazon Expeditions trip.

Printed references: