So, you didn't give to much details, but here's what you can try. Add an integer property in you controller and initialize it in the constructor. Increment it each time you press Add button:
public integer x {get; private set;}
public myConstructor()
{ x = 0; }
public void Add()
{ x++; }
Then create some css style and add it conditionally to your row:
<style>
.redClass {
background-color: red;
}
.greenClass {
background-color: green;
}
</style>
<apex:column (...) styleClass="{!IF(x = 0, 'green', 'red')}" />
After page refresh, your counter will always be 0. After each call to Add method it will be greater. You could also create an array of counters to distinguish between separate rows. Also consider adding some nested IF formula to distinguish counter state.
EDIT:
As distinguishing between rows might be the most tricky part, what I would use is <apex:variable value="{!0}" var="index" />, then the <apex:repeat value="{!items}" var="item">, build a table with simple <td> tags, and increment index on each iteration with <apex:variable value="{!index + 1}" var="index" />. This way you can keep track on each row in the table from Visualforce. It should be a good starting point.