If you want to change buttons text color (positive, negative, neutral) just add to your custom dialog style:
<item name="colorAccent">@color/accent_color</item>
So, your dialog style must looks like this:
<style name="AlertDialog" parent="Theme.AppCompat.Light.Dialog.Alert">
<item name="android:textColor">@android:color/black</item>
<item name="colorAccent">@color/topeka_accent</item>
</style>