Is there a function that changes the background of an activity in android studio?

You can change the background of the layout that occupies the entire Activity with the setBackgroundColor () method.

For example:

Your XML:

<FrameLayout
    android:id="@+id/root_layout"
    android:layout-width="match_parent"
    android:layout-height="match_parent">
   ...
</FrameLayout>

Your Activity:

FrameLayout rootLayout = (FrameLayout) findViewById (R.id.root_layout);
rootLayout.setBackgroundColor(Color.parseColor("#ffffff"));