[android] How to change DatePicker dialog color for Android 5.0

The reason why Neil's suggestion results in a fullscreen DatePicker is the choice of parent theme:

<!-- Theme.AppCompat.Light is not a dialog theme -->
<style name="DialogTheme" parent="**Theme.AppCompat.Light**">
    <item name="colorAccent">@color/blue_500</item>
</style>

Moreover, if you go this route, you have to specify the theme while creating the DatePickerDialog:

// R.style.DialogTheme
new DatePickerDialog(MainActivity.this, R.style.DialogTheme, new DatePickerDialog.OnDateSetListener() {
    @Override
    public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
        //DO SOMETHING
    }
}, 2015, 02, 26).show();

This, in my opinion, is not good. One should try to keep the styling out of java and inside styles.xml/themes.xml.

I do agree that Neil's suggestion, with a bit of change (changing the parent theme to say, Theme.Material.Light.Dialog) will get you the desired result. But, here's the other way:

On first inspection, we come across datePickerStyle which defines things such as: headerBackground(what you are trying to change), dayOfWeekBackground, and a few other text-colors and text-styles.

Overriding this attribute in your app's theme will not work. DatePickerDialog uses a separate theme assignable by the attribute datePickerDialogTheme. So, for our changes to take affect, we must override datePickerStyle inside an overriden datePickerDialogTheme.

Here we go:

Override datePickerDialogTheme inside your app's base theme:

<style name="AppBaseTheme" parent="android:Theme.Material.Light">
    ....
    <item name="android:datePickerDialogTheme">@style/MyDatePickerDialogTheme</item>
</style>

Define MyDatePickerDialogTheme. The choice of parent theme will depend on what your app's base theme is: it could be either Theme.Material.Dialog or Theme.Material.Light.Dialog:

<style name="MyDatePickerDialogTheme" parent="android:Theme.Material.Light.Dialog">
    <item name="android:datePickerStyle">@style/MyDatePickerStyle</item>
</style>

We have overridden datePickerStyle with the style MyDatePickerStyle. The choice of parent will once again depend on what your app's base theme is: either Widget.Material.DatePicker or Widget.Material.Light.DatePicker. Define it as per your requirements:

<style name="MyDatePickerStyle" parent="@android:style/Widget.Material.Light.DatePicker">
    <item name="android:headerBackground">@color/chosen_header_bg_color</item>
</style>

Currently, we are only overriding headerBackground which by default is set to ?attr/colorAccent (this is also why Neil suggestion works in changing the background). But there's quite a lot of customization possible:

dayOfWeekBackground
dayOfWeekTextAppearance
headerMonthTextAppearance
headerDayOfMonthTextAppearance
headerYearTextAppearance
headerSelectedTextColor
yearListItemTextAppearance
yearListSelectorColor
calendarTextColor
calendarSelectedTextColor

If you don't want this much control (customization), you don't need to override datePickerStyle. colorAccent controls most of the DatePicker's colors. So, overriding just colorAccent inside MyDatePickerDialogTheme should work:

<style name="MyDatePickerDialogTheme" parent="android:Theme.Material.Light.Dialog">
    <item name="android:colorAccent">@color/date_picker_accent</item>

    <!-- No need to override 'datePickerStyle' -->
    <!-- <item name="android:datePickerStyle">@style/MyDatePickerStyle</item> -->
</style>

Overriding colorAccent gives you the added benefit of changing OK & CANCEL text colors as well. Not bad.

This way you don't have to provide any styling information to DatePickerDialog's constructor. Everything has been wired properly:

DatePickerDialog dpd = new DatePickerDialog(this, new DatePickerDialog.OnDateSetListener() {
    @Override
    public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {

    }
 }, 2015, 5, 22);

 dpd.show();