[Legend Android Development] lyka:
2.03 Roms have a broken vanilla lockscreen which look like this:

This lockscreen has the trasparency and can be changed editing keyguard_screen_tab_unlock.xml in framework-res.apk (You need to deassemble with apktool).

You can change color and trasparency by changing the ARGB color highlighted down here.

If you refer to CyanogenMod or other Vanilla (from source) i can't confirm that changing the highlighted part of that xml will help (i don't know if there is a class which create the RelativeLayout and apply a background somewhere outside the xml) .

<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout android:gravity="center_horizontal" android:id="@id/root" [B]android:background="#DC000000"[/B] android:layout_width="fill_parent" android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tabunlock="http://schemas.android.com/apk/res/com.android.tabunlock">
<TextView android:textAppearance="?textAppearanceMedium" android:ellipsize="marquee" android:gravity="bottom|right|center" android:id="@id/carrier" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="10.0dip" android:layout_marginRight="8.0dip" android:singleLine="true" android:layout_alignParentTop="true" android:layout_alignParentRight="true" />
<com.android.internal.widget.DigitalClock android:id="@id/time" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="20.0dip" android:layout_marginTop="52.0dip" android:layout_marginBottom="10.0dip" android:layout_below="@id/carrier">
<TextView android:textAppearance="?textAppearanceMedium" android:textSize="72.0sp" android:gravity="bottom" android:id="@id/timeDisplay" android:layout_width="wrap_content" android:layout_height="wrap_content" android:shadowColor="#c0000000" android:shadowDx="0.0" android:shadowDy="0.0" android:shadowRadius="3.0" />
<TextView android:textAppearance="?textAppearanceMedium" android:textSize="22.0sp" android:gravity="bottom" android:id="@id/am_pm" android:layout_width="wrap_content" android:layout_height="fill_parent" android:layout_marginLeft="8.0dip" android:layout_marginBottom="-6.0dip" android:singleLine="true" android:shadowColor="#c0000000" android:shadowDx="0.0" android:shadowDy="0.0" android:shadowRadius="3.0" />
</com.android.internal.widget.DigitalClock>
<TextView android:textAppearance="?textAppearanceMedium" android:id="@id/date" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="24.0dip" android:layout_below="@id/time" />
<TextView android:textAppearance="?textAppearanceMedium" android:id="@id/status1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="24.0dip" android:layout_marginTop="4.0dip" android:drawablePadding="4.0dip" android:layout_below="@id/date" />
<TextView android:textAppearance="?textAppearanceMedium" android:id="@id/status2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="24.0dip" android:layout_marginTop="4.0dip" android:drawablePadding="4.0dip" android:layout_below="@id/status1" />
<TextView android:textAppearance="?textAppearanceMedium" android:id="@id/screenLocked" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="24.0dip" android:layout_marginTop="12.0dip" android:layout_below="@id/status2" />
<com.android.internal.widget.SlidingTab android:orientation="horizontal" android:id="@id/tab_selector" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginBottom="80.0dip" android:layout_alignParentBottom="true" />
<Button android:id="@id/emergencyCallButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="24.0dip" android:layout_marginTop="8.0dip" android:drawableLeft="@drawable/ic_emergency" android:drawablePadding="8.0dip" android:layout_below="@id/screenLocked" style="@style/Widget.Button.Transparent" />
</RelativeLayout>