[Vuejs]-Change background color in vue.js based on a class name

new Vue({
  el: "#app",
  data: {
  	bgColour: 'blue',
    classes: [ 'blue', 'red', 'green'
    ]
  }
})

body {
  background: #fff;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

.blue {
  background: blue;
}

.red {
  background: red;
}

.green {
  background: green;
}

<div id="app" :class="bgColour">
  <select v-model="bgColour">
    <option v-for="myClass in classes" :value="myClass">{{ myClass }}</option>
  </select>
</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>