Highliting Section of a Still Image (screen grab)?

Been trying like crazy to figure out what I thought would be a simple effect:

I have a screen grab of a webpage positioned above the main timeline. It has a bit of text, there
is a voice over reading some of the the text.

I want to quickly highlight a particular word here and there to match the voice over. So, for instance,
The VO says "First there is GREEN..." (and I want to have a flash of green come up to highlight just the word
"green" in the text. Then the VO says "Next there is RED" and I want a quick flash of red to flare up over
the word "red" on the screenshot... etc.

I've tried shape masking with keyframes every which way I can think of while changing the color control, but I can't get the effect. The color flash just comes on and doesn't change.

Any suggestions would be greatly appreciated.

Thank you!

Steve

Shape generator, only on that section of the VO, set color and transparency. Should be very easy.

Thank you! I eventually found a more involved solution, but this gives me another option and more flexibility.

Not *exactly* the same thing, but I also like Simon Ubsdell's TKY Marker Pen - a free Title that provides animated markers that could be made to work as highlighter effects:

www.fcp.co/forum/text-titles/15591-free-...ffect-tky-marker-pen