This is the style used for any ActionMode, I pulled it from the SDK. You’ll need to create your own style to customize it. It’s really easy to do. If you’ve never done anything like this before, you should read through this post on customizing the ActionBar. It explains everything you’ll need to know.
<style name="Widget.ActionMode">
<item name="android:background">?android:attr/actionModeBackground</item>
<item name="android:backgroundSplit">?android:attr/actionModeSplitBackground</item>
<item name="android:height">?android:attr/actionBarSize</item>
<item name="android:titleTextStyle">@android:style/TextAppearance.Widget.ActionMode.Title</item>
<item name="android:subtitleTextStyle">@android:style/TextAppearance.Widget.ActionMode.Subtitle</item>
</style>