Style the NumberPickers in SpinnerDatePicker
masterThe SpinnerDatePicker is composed of three NumberPickers. You can customize their appearance (such as text size, color, and divider colors) by passing a style resource to .spinnerTheme() in the builder.
Define your style in res/values/styles.xml. Use android:colorControlNormal to control the color of the horizontal dividers in the NumberPicker.
<!-- res/values/styles.xml -->
<style name="NumberPickerStyle">
<item name="android:textSize">22dp</item>
<item name="android:textColorPrimary">@color/colorAccent</item>
<item name="android:colorControlNormal" tools:targetApi="lollipop">@color/colorAccent</item>
</style>