Thanks for your reply.
I am using the silverlight viewer application template and configured the map using the app builder.
In it I have a feature layer which comes with a default symbology, with outline, fill color, and selection color.
In the builder, I have control over the outline color and fill color, but not the selection color.
I do a query against this feature layer to return the graphics which I use to build a graphicslayer.
The symbology seems to be based on the feature layer symbology.
I can override the selection color the "feature" layer in the code using the SelectedColor property.
For the graphicslayer I used the above procedure, but it seems to reset itself to what it was before I apply the templated symbology.