It seems maybe I took the wrong approach. I followed the instructions I found on the forums and just adjusted for the recent release.
I guess it didn't occur to me to look at the Silverlight docs because the last time I looked there was hardly anything there concerning custom themes (that was a while ago).
Basically, what I wanted to do was make some modifications to the Office Blue theme. But, I wanted those modifications to be part of source control in our project. I didn't want to just modify the Office Blue, rebuild it, and then reference it as a DLL in the app. I'm sure there will be more tweaks to make in the future and I thought it made sense to have a custom theme as part of the source of the project.
If I modify things to use the pattern in the second link you sent, how would I set things up to default to the Office Blue theme if things aren't found in mine?
Just so you know, the basic modifications I am currently looking to make are in the roll-over colors for the menus, disabled view of combo boxes, and maybe a few minor color changes in the GridView. I was also experimenting with changing the ReadOnly state of the TextBox so it looked like a label. I was doing this by getting rid of the border and making the background transparent, but control was still highlighting and turning white when I clicked on it, and I wasn't sure where that was coming from.
Thanks for your help!