Elevation

That "shaded line" that concerns you is elevation . You can remove it by setting its value to 0dp . So your code would look like this:

<android.support.v7.widget.Toolbar
       xmlns:app="http://schemas.android.com/apk/res-auto"
       android:id="@+id/my_awesome_toolbar"
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:background="?attr/colorPrimary"
       android:elevation="0dp"
       android:minHeight="?attr/actionBarSize"
       app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
       app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

Transparent Toolbar

Regarding transparency, one way you can do this is to work with your style . All you need to do is set the theme that hides toolbar , set the action bar style with transparent background, and set this style to widget of the toolbar.

<style name="Theme.Custom" parent="@android:style/Theme.AppCompat">
    <item name="windowActionBar">false</item>
    <item name="windowActionBarOverlay">true</item>
    <item name="android:windowActionBarOverlay">true</item>
</style>

<style name="CustomActionBar" parent="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
    <item name="android:windowActionBarOverlay">true</item>
    <!-- Support library compatibility -->
    <item name="windowActionBarOverlay">true</item>
</style>

Transparent Layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- Toolbar should be above content-->
    <include layout="@layout/toolbar" />

</RelativeLayout>

Toolbar Layout

<android.support.v7.widget.Toolbar
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:theme="@style/CustomActionBar"/>

Another way would look like this:

You can set the background for Android, the transparent color pattern, which works great. Add this to the layout you want a transparent toolbar:

android:background="@android:color/transparent"

If you want to change the alpha programmatically, you can modify the alpha in the background of the toolbar itself. Just get an instance of drawable and set alpha :

mToolbar = findViewById(R.id.my_toolbar);
mToolbar.getBackground().setAlpha(0);