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1. Select the text.

2. Click the "Fonts" button.

3. Use the "document color" button (4th button from the left) to adjust.
 
Sounds awfully PowerPointish... Keynotes are designed to be sexy, not have a solid color text box. You could always insert a shape (square) behind the text box if you really wanted to.
 
Here's how I did it.

iWork '09

On the upper right is i button (inspector)

Clicked that on got a box

Two buttons Transition and Appearance

Appearance
Body
Background
Color fill
then I picked a color

Yes it is Powerpointish but just want basic information to be more like a billboard rather than a fireworks display.

Also I am using the same basic header information and copying the basic slide to build on was super easy. Now if I can figure out how to save it so the individual slides will usable in iMovie I will be golden!
 
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