Android : Eclipse complaining about android layout xml file

So I'm new to android and am working through the tutorial found here http://www.vogella.com/tutorials/Android/article.html#firstandroidapp, and am at the part where it asks me to change the backgroud color to silver. When I inserted android:silver="#C0C0C0", it was giving me the error shown below and it is still giving me the same error even after I remove the line.

error: No resource identifier found for attribute 'backGround' in package 'android'

So this is my activity_main.xml file.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.harish.firstapp.MainActivity" >

    <EditText
        android:id="@+id/main_input"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="62dp"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/main_input"
        android:layout_below="@+id/main_input"
        android:layout_marginLeft="67dp"
        android:layout_marginTop="59dp"
        android:text="Start"
        android:onClick="onClick" />

</RelativeLayout>

P.S. I have already tried restarting Eclipse but it still keeps complaining.