The Telerik Theme class is missing an iterator for the used colors in the theme. With such an iterator it would be much easier to use the color blend feature.
As an extension i would like to suggest to have a getter/setter for a colorpalette which contains all the used colors of a theme. The advantage of the colorpalette is it could have an iterator for the colors, be loaded/saved to xml and it could be easily used with every theme. When i define a green colorpalette i could use it with the desert theme, the office 2007 blue theme, the aqua theme, ...
As a further side effect telerik could provide predefined colorpalettes like a silver and a black colorpalette and then we would not need the office2007black and office2007silver theme anymore. We would just change the colorpalette to silver or black.