Change ActionBar title text color using Light.DarkActionBar theme in AppCompat 21

You can change it with actionBarStyle attribute of theme.

<style name="AppBaseTheme" parent="@style/Theme.AppCompat.Light.DarkActionBar">
    <item name="actionBarStyle">@style/MyActionBar</item>
</style>

<style name="MyActionBar" parent="@style/Widget.AppCompat.ActionBar.Solid">
    <item name="titleTextStyle">@style/MyTitleTextStyle</item>
</style>

<style name="MyTitleTextStyle" parent="@style/TextAppearance.AppCompat.Widget.ActionBar.Title">
    <item name="android:textColor">CHANGE_COLOR_HERE</item>
</style>

This will make your Toolbar Title use white color:

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

To understand what is the difference between ThemeOverlay.AppCompat.Dark.ActionBar and Theme.AppCompat.Light.DarkActionBar check this answer

It's app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" that applies a light colour because the title colour which is used in this theme is white.

make sure you make the changes in all your values folder, like 'values-v11', 'values-v14' etc.. if it exists.

Else make sure the same 'AppTheme' you shown above is being used in the app.

Please post you full style.xml and the manifest code referring the style which will give more insights on your problem.

Also you can try setting app:theme and app:popupTheme attributes on you ToolBar.