You can have Numbers change the appearance of a cell or its text when the value in the cell meets certain conditions. For example, you can make cells turn red if they contain a negative number. To change the look of a cell based on its cell value, create a conditional highlighting rule.
Select one or more cells.
Tap 
, tap Cell, then tap Add Conditional Highlighting.
Tap a type of rule (for example, if your cell value will be a number, tap Numbers), then tap a rule.
Enter values for the rule.
For example, if you selected the rule “date is after”, enter a date that the date in the cell must come after.
Tap 
to use a cell reference. A cell reference lets you compare the cell’s value to another cell — so, for example, you can highlight a cell when its value is greater than another cell’s. Tap a cell to select it, or enter its table address (for example, F1). Tap 
when you’ve finished.
Tap a text style, such as bold or italic, or a cell fill, such as red or green.
You can choose Custom Style to choose your own font colour, font style and cell fill.
Tap Done.
Note: If a cell matches multiple rules, its look changes according to the first rule in the list. To reorder rules, tap Edit, then drag 
next to the rule name. Tap Done.
After you add a conditional highlighting rule to a cell, you can apply that rule to other cells.
Select the cell with the rule you want to repeat and the cells you want to add the rule to.
Tap , then tap Cell.
Below Conditional Highlighting, tap Combine Rules.
Select cells with the rules you want to delete.
Tap , then tap Cell.
Below Conditional Highlighting, swipe left on the rule you want to delete, then tap Delete.