background parallax ketiban

kenapa.PNGfoto di belakang background abu2 adalah parallax, namun saya bingung supaya warna abu2nya hilang

index.html

 <h3 class="center">Testimoni</h3>

      <div class="parallax-container">
      <div class="parallax"><img src="img/paralax/par5.png"></div>
        <div class="slider">



    <ul class="slides">
      <li>
        <!-- <img src="img/paralax/par5.png"> --> <!-- random image -->
        <div class="col m4 s12 center-align">
        <div class="caption right-align ">
          <div class="card-panel center-align " style="width: 350px; height: 300px; align-content: right; position: absolute; right: 300px;">
         <i class="material-icons medium " style="color: black;">face</i>
          <h5 class="">Al Gifari</h5>
          <p class="">"Bahannya bagus enak dan nyaman dipakai"</p>
        </div>
        </div>
      </div>
      </li>
      <li>
        <!-- <img src="img/paralax/par5.png"> --> <!-- random image -->
        <div class="col m4 s12 center-align">
        <div class="caption center-align darken grey-text text-darken-3">
          <div class="card-panel center-align " style="width: 350px; height: 300px; align-content: right; position: absolute; right: 300px;">
         <i class="material-icons medium " style="color: black;">face</i>
          <h5 class="darken grey-text text-darken-3">Alwi </h5>
          <p class="darken grey-text text-darken-3">"Design nya keren dan kekinian banget!"</p>
        </div>
        </div>
      </div>
      </li><li>
       <!--  <img src="img/paralax/par5.png">  --><!-- random image -->
        <div class="col m4 s12 center-align">
        <div class="caption left-align darken grey-text text-darken-3">
          <div class="card-panel center-align " style="width: 350px; height: 300px; align-content: right; position: absolute; right: 300px;">
         <i class="material-icons medium " style="color: black;">face</i>
          <h5 class="darken grey-text text-darken-3">Wardhanoffzen</h5>
          <p class="darken grey-text text-darken-3">"Sablonannya berkualitas dan harganya terjangkau"</p>
        </div>
        </div>
      </div>
      </li>
</ul>
</div>
</div>
</div>
  </div>