Making background fade

[Karl]

Hi,

I have to tidy up some PowerPoints for a client. He's used the wrong font
throughout, but when I change the font I also lose a crucial effect on some
slides.

The slides in question all start by posing a question using black text on a
white background. When you play the slideshow, the next action is for a blue
box, containing the answer, to appear overlaid on the original question. As
the blue box appears, the question text fades to a very light grey.

As soon as I change the font, the "fade to grey" effect dissappears.

Can anyone tell me how to either stop it dissappearing or to reapply it?

Thanks

Karl