Hi @prasannaamle30,
My example was just to show how you could use HTML in a Select. You could also use the expression you used earlier in that same type of setup.
I have adapted my example to use your number expression instead. Also updated it to use a concat function as well (makes copy/pasting into the expression tab a bit easier)
Can you try the below in the Select instead? (add via expression tab)
concat('<p style="color:', if(empty(item()?['Customer Due Date']),null,if(less(addDays('1899-12-30',int(item()?['Customer Due Date']),'yyyy-MM-dd'), utcNow()), 'red', 'green')), '">', if(empty(item()?['Customer Due Date']),null,addDays('1899-12-30',int(item()?['Customer Due Date']),'yyyy-MM-dd')), '</p>')