Forms :: Conditional Formatting Of Currency Field In Entry Form

I have some Conditional Formatting of a Currency Field in an Entry Form. The cell is conditionally formatted with a yellow background when the value is zero.

I now wish to add an additional condition to the expression such that even if the value is zero it will not be formatted if a specific check box is TRUE.

I have tried modifying the expression such that it reads;

[currency field]=0 AND [check box]<>TRUE.

It correctly turns off the conditional formatting if the check box is ticked, but does not turn it on again when the check box is unticked.