While working on a custom module for a Rainbow installation, I recently ran into a new kind of issue. I created an 'edit' page for my module, deriving it from the Rainbow.UI.AddEditItemPage class.
When viewed in the browser, this new page lacks all of the css properties...no colors or fonts to match the rest of the portal.
The solution, it turns out, is that the <head> tag on that page must be told to run at the server...i.e....
This: <head runat="server"></head>
Not This: <head></head>
This allows the CSS link to be injected when the page is called.