Change Vue element style according to data value

In my HTML page, I have a table that lists information about purchase applications and there is a status column. I would like to change the color of the text according to the value of the status.

For example, if the purchase application is validated, I want the "Validated" to be green. But if the purchase application is declined, I want the "Declined" to be red.

My html code :

<!DOCTYPE html>
<html lang="fr">
  <head>
    <meta charset="utf-8">

    <link rel="stylesheet" type="text/css" href="./index.css">
  </head>
  <body>
      <table>
          <tr>
            <th>Demande n°</th>
            <th>Etat</th>
            <th>N° Commande</th>
          </tr>
          <tr v-for="demande in demandes">
            <td>{{demande.numDemande}}</td>
            <td v-bind:style="{ color: activeColor}">{{demande.etatDemande}}</td>
            <td>{{demande.numCommande}}</td>            
          </tr>
        </table>
    </div>
    <script type="text/javascript" src="/Achats/vue.js"></script>
    <script type="text/javascript" src="/Achats/vue-resource.min.js"></script>
    <script type="text/javascript" src="index.js"></script>
  </body>
</html>

My js code :

window.onload = function () {
  var consultationAchats = new Vue({
    el: "#body",
    data: {
      demandes: [],
      activeColor: 'orange'
    },
    methods: {
      getDemandes: function() {
        this.$http.get("/getDemandes").then(function(response) {
          if (response.body) {
            consultationAchats.demandes = response.body;
          }
        })
      },
      styleEtat: function(etat) {
        if (etat == "En attente de traitement") {
          this.activeColor = 'orange';
        } else if (etat == "En cours de traitement") {
          this.activeColor = 'orange';
        } else if (etat == "Refusé") {
          this.activeColor = 'red';
        } else if (etat === "Validée") {
          this.activeColor = 'green';
        }
      }
    },
    created: function() {
      this.getDemandes();
    }
  })

I tried to use the v-bind:style and defined the color into variable activeColor that will be changed in function styleEtat. But I realised that I don't know how or where I can use the function.