How to use/evoke to set in computed through methods? - vue.js

Question

I am trying to update data property through computed property and found that it is impossible to set the value but I can use get/set to assign value in data property. Please see my example first.
data () {
return {
title: '',
color: null
}
},
computed: {
isTitle: {
get () {
return this.title
},
set () {
console.log('how can I come to this line?')
this.title = 'update title example'
}
},
isTitle() {
this.color = 'red'
return 'update title example'
}
},
mounted () {
this.getAccessToTitle()
},
methods: {
getAccessToTitle () {
if (isTitle) {
this.color = 'red'
}
},
example looks little bit weird but what I wanted to ask is..
when getAccessToTitle() is called through mounted, I assume, isTitle's set() should update the title in data property isn't it? I am not sure how can I use set in computed property when I call isTitle through methods but not template(I saw many examples that use template to call computed like https://vuejs.org/guide/essentials/computed.html#writable-computed but it is not what I am looking for!)
Thank you
this is what I wanted to do originally. update color in data and return title in isTitle. Tt works but was told that it is bad way to use computed so I added get/set
data () {
return {
title: '',
color: null
}
},
computed: {
isTitle() {
this.color = 'red' <---
return 'update title example' <---
}
},
mounted () {
this.getAccessToTitle()
},
methods: {
getAccessToTitle () {
if (isTitle) {
isColor(this.color)
}
},
isColor(val) {
// do something...
}