Screen background changing when phone is tilted horizontal

[IndyG]

In the android app I am developing I have given the background of one color. When the phone is tilted horizontal the screen background changes to a lighter version of the previous color?What to do, to avoid this?\[code\]<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#228b22" androidrientation="vertical" >\[/code\]