Mystery solved! My mystery Dove is a common Mourning Dove. In a recent e-mail from the Stokes' (Stokes Field Guide to the Birds of North America) they give this explanation:
"In our guide we list all known hybrids that have occurred in the wild at the end of each account. If there are none listed, then there are no known occurrances. Thus, there are no known hybrids between White-winged and Mourning Doves. This listing of hybrids is unique to our guide and a nice feature in cases like this.
I believe that the lighter area is due to the wing being tucked under the feathers at the side of the breast, pushing them out so that they are reflecting the light more. White-winged Doves have white along the edge of the wing and not along the side of the breast; they also have no dark spots on the wing coverts, and they have a longer, slightly downcurved bill. This bird does seem to have a shorter tail, but Mourning Doves can also be molting or have lost their central tail feathers temporarily, as seems to be the case with this bird."
Don and Lillian
The Stokes' have just released their new Eastern and Western Field Guides and there are quite a few changes from the old guides - definitely worth the upgrade!