<div class="input">
	<input class="input-control" id="input" placeholder="hogehoge" />
	<label class="input-label" for="input">入力すると色が変わります</label>
</div>
.input-label {
  color: blue;
}
.input :not(*):placeholder-shown, .input-label {
  color: green;
}
.input-control:placeholder-shown ~ .input-label {
  color: red;
}

External CSS

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External JavaScript

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