How to add a button to that script? Or other solutions?

Hi everyone! I have a problem with my color changing script. The color of the object is not only changing when I tap on the object but also when I tap around the object. So what I need, is a limited area on the screen where I can tap on, to change the color (even if it is just a button on which I have to tap on (or if any of you may have an idea for that, a tap trigger set on the object)). If any of you could help me I´d be really thankful.

 public class ColorChange : MonoBehaviour
 {
     public Color[] colors = new Color[] { Color.red, Color.blue, Color.green, Color.yellow };
     public int currentColor, length;
     private string CurrentColor;
     
     private void Start()
     {
         currentColor = 0;
         CurrentColor = string.Empty + currentColor;
         length = colors.Length;
         GetComponent<Renderer>().material.color = colors[currentColor];
     }
 
     private void Update()
     {
         if(MobileInput.Instance.Tap)
         {   
             Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             RaycastHit hit;
             if (Physics.Raycast(ray, out hit, 5))
             {
                 currentColor = (currentColor + 1) % length;
                 GetComponent<Renderer>().material.color = colors[currentColor];
             }
         }
     }
 }