Grey out completed questions

Hi All,

I have a short quiz of four questions that works fine. I have a variable for each question that is set to true when submitted so that the story knows to move to the final slide when completed.

I wanted to use these variables to also show a greyed-out version of the question as feedback on the main slide so the user knows they have completed that question. It does not seem to work. 

I assume  I can use a variable more than once and get the current value to change the state of a hidden caption? Can I use a trigger in one slide to change the state of an object in another slide?

Thanks

Paul