android Theme.Holo.Dialog changing blue lines to orange

Just dug around in the source for you - unfortunately the Divider line in the dialog layouts is a view with a hard coded color background that doesn't reference any themes:

<View android:id="@+id/titleDividerTop"
  android:layout_width="match_parent"
  android:layout_height="2dip"
  android:visibility="gone"
  android:background="@android:color/holo_blue_light" />

So if you want to change the color you'll have to layout your own, custom, dialog box. to make it easier, it wouldn't hurt to just copy from the android source base and customize it to your needs, but you might also get a lot more than you need.

There is a library which does exactly what you need - easy styling of dialogs in Holo theme:

https://github.com/inmite/android-styled-dialogs