Fragments not opaque during animation - animation

Question

I have searched on stackoverflow and google but could not find a solution to a simple problem.
I have a fragment on the screen and want to make a new fragment slide in from below in such a way that the old fragment is slowly covered up during the animation until it is no more visible.
The problem I have, is that the fragment sliding in is transparent during the animation, i.e. you can see the fragment below. I want the fragment sliding in to be completely opaque. How can I achieve that?
I have already set the background of both fragments to a specific color but it did not solve the problem.
Here is my code.
Fragment sliding in:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="#dimen/std_margin"
android:background="#color/fragment_background" >
</RelativeLayout>
In the activity:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.setCustomAnimations(R.anim.slide_in_up, R.anim.fade_out);
String tag = backStack.peek();
BaseFragment top = (BaseFragment) getSupportFragmentManager().findFragmentByTag(tag);
ft.detach(top);
String tag2 = UUID.randomUUID().toString();
ft.add(android.R.id.content, fragment, tag2);
backStack.push(tag2);
ft.commit();