SOURCE

<div id="app">
	<div class="demo"  @click="GetRed=!GetRed" :class="disclass">
	</div>

	<br>

<div class="demo"  @click="GetRed=!GetRed"
 :class="{red:GetRed}">
</div>
</div>
<script>
	new Vue({
            el:"#app",
            data:{
                GetRed:false,
            },
            computed:{
                disclass:function()
                {
                    return{
                        red:this.GetRed,
                        blue:!this.GetRed
                    };
                },
            }
        });
</script>

.demo{
    width:100px;
    height:100px;
    background-color: grey; 
}
.red{
   background-color: red; 
}
.blue{
   background-color: blue; 
}