Basic panel can be used in the layers BG and FG.

Source code:

<!--
Basic panel type of pattern.
-->
<SkinObject><Type>BasicPanel</Type>
    <!--
    Globally unique name. No other object in the <Skin>
    section can have the same name.
    Obligatory parameter.
    -->
    <Name>Background</Name>

    <!--
    Object visibility.
    Default value - true;
    -->
    <Visible>true</Visible>

    <!--
    Object position.
    Left and Top must always be specified.
    If Right is not specified then Width must be specified instead.
    If Bottom is not specified then Height must be specified instead.
    See http://mirror3.cze.cz/radicalchat/documentation/rpsf.pdf.
    Obligatory section.
    -->
    <Position>
        <!--
        Left position of the object.
        -->
        <Left>0%+0, min=-10000, max=10000</Left>

        <!--
        Top position of the object.
        -->
        <Top>0%+0, min=-10000, max=10000</Top>

        <!--
        Width of the object.
        If Width is not set then Right is used instead.
        -->
        <!--<Width>100</Width>-->

        <!--
        Height of the object.
        If Height is not set then Bottom is used instead.
        -->
        <!--<Height>100</Height>-->

        <!--
        Right position of the object.
        -->
        <Right>100%-100, min=-10000, max=10000</Right>

        <!--
        Bottom position of the object.
        -->
        <Bottom>100%-100, min=-10000, max=10000</Bottom>
    </Position>

    <!--
    Look and feel.
    Obligatory section.
    -->
    <LookAndFeel>
        <!--
        Pattern specifies the repeatable seamless texture.
        <Pattern><Image> can be absolute or relative
        path to the texture. Supported formats png, jpeg, gif.
        Obligatory parameter.
        -->
        <Pattern>
            <Image>./skin/images/walltexture.jpg</Image>
        </Pattern>

        <!--
        AlphaBlend also known as transparency.
        Double value - from 0 to 1.
        Default value - 1.
        -->
        <AlphaBlend>0.75</AlphaBlend>

        <!--
        Similar to Adobe Photoshop blend mode.
        Could be one of the following values
        normal, layer, multiply, screen, lighten, darken,
        difference, add, subtract, invert, alpha, erase,
        overlay, hardlight.
        See http://help.adobe.com/en_US/AS3LCR/Flash_10.0/flash/display/DisplayObject.html#blendMode.
        Default value - normal.
        -->
        <BlendMode>normal</BlendMode>

        <!--
        Color transformation.
        Optional section.
        -->
        <ColorTransform>
            <!--
            brightness
            Number -The percentage to apply the brightness
            channel between -1 and 1, where -1 is completely
            black and 1 is completely white.

            tintColor
            Hexadecimal - A hexadecimal color value representing
            the color to apply.

            tintMultiplier
            Number - A decimal value between 0 and 1
            representing a percentage to apply with
            the tintColor value.

            redMultiplier
            Number - The percentage to apply the color,
            as a decimal value between 0 and 1.

            greenMultiplier
            Number - The percentage to apply the color,
            as a decimal value between 0 and 1.

            blueMultiplier
            Number - The percentage to apply the color,
            as a decimal value between 0 and 1.

            alphaMultiplier
            Number - A decimal value between 0 and 1
            representing a percentage to apply
            the alpha transparency channel.

            redOffset
            Number - A number from -255 to 255
            that is added to the red channel value after
            it has been multiplied by the redMultiplier value.

            greenOffset
            Number - A number from -255 to 255
            that is added to the green channel value
            after it has been multiplied
            by the greenMultiplier value.

            blueOffset
            Number - A number from -255 to 255
            that is added to the blue channel value
            after it has been multiplied
            by the blueMultiplier value.

            alphaOffset
            Number - A number from -255 to 255
            that is added to the alpha channel value
            after it has been multiplied
            by the alphaMultiplier value.
            -->
            <Color
                redMultiplier="0.1" greenMultiplier="0.5" blueMultiplier="0.8" alphaMultiplier="1"
                redOffset="128" greenOffset="128" blueOffset="128" alphaOffset="0"
            />

            <!--
            Or developer can use a tint.
            -->
            <!-- <Color brightness="0" tintColor="0xFF000000" tintMultiplier="0" /> -->
        </ColorTransform>
    </LookAndFeel>
</SkinObject>