Highlight (fill colour) in fields when duplicate number value entered on a form....

You can use a document level script like the example below. In my example below, I  created a function named "numberPage()".

As you can observe, I also declared my variables, in which variable "g" represents  "NUMBER_PAGEX.X.XX" as the parent field that will be used in the getArray() method..

Just change the parent field name  to whatever needs to be applied in the children fields

function numberPage() {

var g = this.getField("NUMBER_PAGE1.1");

var a = g.getArray();

for (i =0; i < a.length; i++) { 

if ( (event.target.name !== a[i].name) && (event.target.value !== a[i].value) ) event.target.fillColor = color.transparent;

if ( (event.target.name == a[i].name) && (event.target.value == a[i].value) ) event.target.fillColor = color.red;

 }
}

And just call the function from the fields that you want this event to happen. To do so just place the line below as custom calculation script:

numberPage();

In the script avbove I am using as template  some of the guidance found in the Adobe Acrobat SDK  JavaScript™ for Acrobat® API Reference