Using official 2.57 version for Windows, Both x32 and x64. Video card Nvidia GF GTX 260. OS Win XP x64.

Using the standard start file with a camera, lamp and a cube...

1. Enable GLSL for the 3d viewport and textured shading.
2. Set the diffuse color of the material for the Cube to bright red.
3. Add generated image texture with bright green color.
4. Drag the slider controlling the influence of the texture over the solid diffuse color of the material underneath - you can see the update from green to red in real time in the viewport.
5. Now animate the value - key the color influence of the texture from 0.0 to 1.0 for some frames.
6. Drag the time slider to playback the animation - nothing changes in the viewport but the value in the UI changes also the rendered image.