Please have a look:
http://www.plantuml.com/plantuml/uml/JOv13i9G24JtSmekq2iqlGeAyHCj6ZwDYwPtbwP6o-hn29EPUdBaCZ_Gx-Ol3fwfiSixB5ETCXO5mCDuWJzJAUpM4bXNN8THpexs-QKSwodg4DQfNhxiJUkc0dNPjMBR_ZmLLR4F
I guess, that since we already inherit some parameters within embedded diagrams we should inherit this one, and may be other params too. Though we probably would want to have an ability to disable inheritance from the parent diagram via a new skinparam. What would you think?
A related question is:
http://forum.plantuml.net/8863/skinparam-notebackgroundcolor-honored-embedded-diagram