Nathan and I have talked a lot about color palettes, complementary colors and stuff like that in the past, so I'm not going to say anymore about that here. However, I did want to present an idea that might be interesting to you in certain cases.
Sometimes, it is desirable to create a certain "brand" for an application. Perhaps it is a CRM suite or some other application that you want to make a little unique. One way you can accomplish this in a fairly easy and unobtrusive way is to use the real estate of the action bar to display a logo, picture, etc. Here's an example...
A Close Up
Now that's just a quick example I threw together to demonstrate the idea. Normally, I'd use a more subtle color and graphic. Here's an shot from a real application, in this case my modified document library template.
Another Close Up
Adding this image to the action bar is very easy. Probably most of you know that in the Action Bar properties, you can specify an image resource that will be used for the background of the action bar. If you want to align the image along the right edge as I have done here, there are a few requirements:
1. Make sure that the graphics that you place within the image are in the last 1/3 of the total image width.
2. Select "Center Based Tiling" as the Repeat option.
3. Adjust the height of your action bar as necessary.
OK...that first requirement is strange, but it works.
As soon as you overlap 33% of the width, it leads to undesirable behavior like that shown below.
If you want the color of the action bar to show through, make it a transparent graphic. Here's the same example as before, with a transparent image and the background color of the action bar set to a light purple (yeah it's ugly ;-).
If the image is the correct size, then you can re-size the Notes client window and the image will stay right aligned as you do so. It might take a little playing around with at first, but if you follow the three rules above, this can be a neat little trick to add to your client UI design bag.
P.S. For more action bar fun, check out Kevin Pettitt's much cooler post about Two-Row View Action Bars