IONIC - How to change background button in ionic

How to change background button  in ionic

ion-button in ionic when change background click, but default color change but you want to color of me, then shouldent change color in html or css of ionic.

After i am doing a example ionic change background button you can do the following, to change its color.

Step 1. in file HTML

 <ion-item class="functionClick" lines="none" >
    <ion-button (click) ="pre()" *ngIf="checkPre">
        <ion-img src ="../assets/icon/back.png" ></ion-img>
    </ion-button>
    <ion-button (click) ="next()" [color]="ionicColor">
        <ion-img src ="../assets/icon/next.png" ></ion-img>
    </ion-button>
 
  </ion-item>

Step 2. in file ts

  next(){
   this.ionicColor = "red";
    this.mPosition += 1;
    if(this.mPosition > 0){
      this.checkPre = true;
    }else if(this.mPosition >=200){
      alert("ban da qua cap 1");
    }
    localStorage.setItem("position",""+this.mPosition);

    this.giaotiep = this.mData[this.mPosition];
  }