test script

need to click on color field, but concrete on following divs: <div class="selectize-control form-control multi"> <div class="selectize-input items not-full has-options">

HTML

<script   src="https://code.jquery.com/jquery-3.1.0.js"   
integrity="sha256-slogkvB1K3VOkzAI8QITxV3VzpOnkeNVsKvtkYLMjfk="
crossorigin="anonymous">
</script>

<body>

<div class="form-group">
  <label class="control-label" for="colors[]">Color</label>
  <select id="colors" class="form-control selectized" multiple="multiple" name="colors[]"  
          tabindex="-1" style="display: none;"></select>
  <div class="selectize-control form-control multi">
    <div class="selectize-input items not-full has-options">
    <input type="text" autocomplete="off" tabindex="" style="width: 4px;">
    </div>
  <div class="selectize-dropdown multi form-control" style="display: none;">
    <div class="selectize-dropdown-content"></div>
    </div>
  </div>
</div>

<div class="form-group">
<label class="control-label" for="sizes[]">Sizes</label>
<select id="sizes" class="form-control selectized" multiple="multiple" name="sizes[]" tabindex="-1" style="display: none;"></select>
<div class="selectize-control form-control multi">
<div class="selectize-input items not-full has-options">
<input type="text" autocomplete="off" tabindex="" style="width: 4px;">
</div>
<div class="selectize-dropdown multi form-control" style="display: none;">
<div class="selectize-dropdown-content"></div>
</div>
</div>
</div>

</body>

JavaScript

$("div.selectize-control).find('div[@class="selectize-input"]').click();