In Inkscape, I'm using the Komika Glaze font, styled like the drop shadows that you might see in a comic book. So, the shapes formed by the font itself should remain black. But, the interiors of the letters are transparent. So, when placed over a colored background, e.g. yellow, it appears as though I'm using a yellow font on a yellow background. How can I easily select the interiors of the letters to fill them with white? For example, in the letter 'o', there are four concentric circles (outside-in): the outside shadow, the interior, the inner shadow, and the inner transparent area. How can I select just the interior, without selecting the inner transparent area?
Seems to me you want to create something similar to what is shown below.
The sample above uses the komika glaze font on top of a red background. Using the original font as-is this will appear as a red font on a red background as you had described. Here's what I did to change the color of the interior sections:
The last step makes helps put the text back together, which is useful is you need to resize or move.