Playground.vue

<template>
  <v-app-bar
    :color="color"
    @scroll="onScroll"
  >
  </v-app-bar>
</template>

<script>
  export default {
    data: () => ({
      color: 'blue',
    }),

    methods: {
      onScroll (scroll) {
        this.color = scroll > 10 ? 'red' : 'blue'
      },
    },
  }
</script>