The solution may seem simple but it took me a while to figure it out so I thought I’d note it here using a blinking function.

  public IEnumerator animateTint(GameObject obj,Color newColour,float speed = 2){
         Color originalColor = newColour;
         Color targetColor = newColour;
 
         Color defaultBtnColor = new Color();
     ColorUtility.TryParseHtmlString (btnColor, out defaultBtnColor);
 
     while (obj.GetComponent<Renderer> ().material.color != newColour) {
 
         Material objMat = obj.GetComponent<Renderer> ().material;
         Color curColour = objMat.color;
 
         if(closeEnough(curColour.r,targetColor.r) && closeEnough(curColour.g,targetColor.g) && closeEnough(curColour.b,targetColor.b) ){
             //objMat.color = newColour;
             print ("change tint "+targetColor);
             if(targetColor == newColour){
                 targetColor = defaultBtnColor;
             }else{
                 yield return StartCoroutine(CoroutineUtil.WaitForRealSeconds(1)); //2
                 targetColor = newColour;
             }
             //yield break;    
         }
 
         buttonCode btnCode = obj.transform.parent.GetComponent<buttonCode> ();
     
         if(btnCode.isBlinking){
         objMat.color = Color.Lerp(curColour,targetColor, speed * Time.deltaTime);
         }else{
                 objMat.color = Color.white;
             yield return null;
         }
         //print ("tinting "+curColour);
 
         yield return null;
     }
 }

The main part is

yield return null;

Other things going on here are converting a hex code string to a Unity colour using. (btnColor is a variable specified previously).

ColorUtility.TryParseHtmlString (btnColor, out defaultBtnColor);