Is it not possible to highlight text in one cell using conditional formatting, by clicking in another cell.

Cell A1 has visible text in it, Cell B1 has white text in it so it appears hidden. When the user clicks in cell A1, I want to conditionally format the text in cell B1 to black, so the user sees it and then when they click any other cell, the text in cell B1 changes to white again, so it appears hidden.

I thought this would be easy using CF but I can't figiure a way to do this?