fix select (#133)

closes #117

Reviewed-on: #133

frontend/allowance-planner-v2/src/app/pages/edit-allowance/edit-allowance.page.html

@@ -28,9 +28,9 @@
 
     <div class="item" *ngIf="isAddMode || goalId != 0">
       <label>Colour</label>
-      <select formControlName="color">
-        <option *ngFor="let color of possibleColors" [value]="color" [style.--background]="color">{{color}}</option>
-      </select>
+      <mat-select [(value)]="selectedColor" formControlName="color" [style.--color]="selectedColor">
+        <mat-option *ngFor="let color of possibleColors" [value]="color" [style.--background]="color">{{color}}</mat-option>
+      </mat-select>
     </div>
 
     <button type="button" [disabled]="!form.valid" (click)="submit()">