res/drawable/tab_unselected.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2014 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License
  -->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
    <!-- Tab underline -->
    <item>
        <shape android:shape="rectangle">
            <solid android:color="@color/tab_underline_color"/>
        </shape>
    </item>
    <!-- Tab background -->
    <item android:bottom="@dimen/tab_underline_height">
        <shape android:shape="rectangle" >
            <gradient
                android:startColor="@color/tab_background_gradient_start_color"
                android:endColor="@color/tab_background_gradient_end_color"
                android:angle="270" />
        </shape>
    </item>
</layer-list>