Conditional Formatting on Parent Level only

Hi,

I've been building a module with a list composed of several children and one parent.

The children can be associated with positive or negative numbers (rate of change).

As a parent, the amount associated to it is the sum of all its children.

I'd like to add conditional format ONLY to the parent to check whether the result is 0 (green cell) or different of 0 (red cell).

How could I proceed?

Many thanks,