Set another color of shader material color in a script?

I have a cloud shader and that shader have a white color, so i whant when i press a button my cloud shader color go slower to a another color that i put

Try this

using System;
using UnityEngine;
using System.Collections;

public class ColorBlend
{
	 public Renderer r;
	 public int materialIndex = 0;
	 public string property = "_Color";
	 [Space]
	 [Header("Debug")]
	 [SerializeField]
	 private float debugTime = 5;
	 [SerializeField]
	 private Color debugColor = new Color(0, 1, 1);
	 [SerializeField]
	 private bool debugSet;
	 
	 private Coroutine blendRoutine;
	 
	 void Update()
	 {
		 if (debugSet)
		 {
			 debugSet = false;
			 SetColor(debugColor, debugTime);
		 }
	 }
	 public void SetColor(Color newColor, float duration)
	 {
		 if (blendRoutine != null) StopCoroutine(blendRoutine);
		 blendRoutine = StartCoroutine(BlendRoutine(newColor, duration));
	 }
	 private IEnumerator BlendRoutine(Color endColor, float duration)
	 {
		 float elapsedTime = 0;
		 Color startColor = r.materials[materialIndex].GetColor(property);
		 while (elapsedTime < duration)
         {
                Color newColor = Color.Lerp(startColor, endColor, Mathf.Clamp01(elapsedTime / duration));
                r.materials[materialIndex].SetColor(property, newColor);
                elapsedTime += Time.deltaTime;
                yield return null;
         }
		 blendRoutine = null;
	 }
}

The main important part is using Lerp over time, and this is a pattern you can use over and over for a bunch of different things. Color.Lerp, Mathf.Lerp, Vector3.Lerp, Quaternion.Slerp etc all take 3 arguments. The first two represent opposite ends of a blend, the third argument is where, in between the first and second item, the blend should be, represented as 0-1, with 0.5 meaning a completely even blend. So when we divide elapsed time by duration, since we won’t let elapsed time ever get bigger than duration, that will always result in a number between 0 and 1, making it perfect for use in a Lerp.