Name of button on click

Create a script for changing button colors, example code below. Then attach this script to a game object on your scene. It can be any game object, say the Main Camera object or even an empty game object. Now for each button that you want to change, you need to complete the OnClick() component section in the inspector for that button, as in your attached image.

In the OnClick() section: Either drag the game object with your attached script into the object field, or, click on the little circle with a dot beside the field and select the game object from the list that appears. Then select the name of the script itself.

Code example, the script is called MyButtonScript and contains the method ChangeButtonColor() that will be invoked by OnClick()

 using UnityEngine;
 using System.Collections;
 using UnityEngine.EventSystems;
 using UnityEngine.UI;
 
 public class MyButtonScript : MonoBehaviour {
 
     public void ChangeButtonColor()
     {
         // gets the button which was pressed
         GameObject btnGameObject =  EventSystem.current.currentSelectedGameObject;  
         ColorBlock btnColors = btnGameObject.GetComponent<Button>().colors;
         
         btnColors.normalColor = Color.red;          // Color of button when not selected
         btnColors.pressedColor = Color.green;       // Color when button is being pressed
         btnColors.highlightedColor = Color.blue;    // Color when button is focused or selected
 
         //Now assign the updated colorBlock back to the button
         btnGameObject.GetComponent<Button>().colors = btnColors;    
     }
 }