i would create two xml drawables one for each state of the btn:(saved to your drawable folder)
rounded_btn_black.xml
<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" 
    android:color="@color/black">
    <size
                android:height="100dp"
                android:width="10dp" />
    <corners
       android:radius="15dp"
         />
     <solid
        android:color="@color/black" />
</shape>
another one for orange just changing the color
and then create a selector xml file rounded_button.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/rounded_btn_black" android:state_pressed="true" />
    <item android:drawable="@drawable/rounded_btn_black" android:state_focused="true" />
    <item android:drawable="@drawable/rounded_btn_orange" android:state_enabled="true" />
    <item android:drawable="@drawable/rounded_btn_orange" />
</selector>
then in your layout:
<Button
        android:id="@+id/login"
        android:layout_width="fill_parent"
        android:layout_height="@dimen/standard_btn_height"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="@dimen/standard_margin"
        android:layout_marginLeft="@dimen/standard_margin"
        android:layout_marginRight="@dimen/standard_margin"
        android:background="@drawable/rounded_button"
        android:text="@string/alreadyRegisterd"
        android:textColor="@color/white" >
    </Button>