This configuration on src/plugins/vuetify.js made sense.

export default createVuetify({
  theme: {
    defaultTheme: '***',
    variations: {
      colors: ['primary', 'secondary'],
      lighten: 5,
      darken: 5,
    },
    themes: {
      //
    },
  },
})

https://vuetifyjs.com/en/features/theme/#color-variations