Dither Pick

In init_data.cpp we have:

	Button(text = "Edit Light Dither Style",
		height = 1.5_em, fitParent = true,
		colSpan = 2,
		onPressFunc = [&]()
		{
			call_edit_dither(local_zinit.dither_type, local_zinit.dither_arg, local_zinit.darkcol, false);
			refresh_dlg();
		}),

So, I guess that's the answer

Quest->Init Data->Vars->Dark Room->Edit Light Dither Style