Image Resize : Maintain Proportions But Fill Negative Space

[eluser]Jim Higgins[/eluser]
Is it possible with the Image Manipulation Class (or some other technique) to resize an image while maintaining the proportions, but to fill in the negative space with a solid color? ... not by wrapping the image in a div with a background color, but adding a fill to the actual image.

So, for example, if I have a set of thumbnail images which should be 100x75 and I have an image with a vertical orientation... so say it's 100x150... and I resize it to fit that 100x75 thumbnail space, but I maintain the proportions and it ends up as a 50x75 image. Can I fill in the 25 pixels to the left and right of the image with a solid color?

Check out the 11th example from the top on this page (100x150, keeping ratio, filling top and bottom)?
http://www.verot.net/php_class_upload_samples.htm

That's basically what I'm trying to do, except this example shows a horizontal image with the top and bottom filled in with a solid color.