toolbar background color in visualforce apex Salesforce

Dear guys..

I had a big issue while working with <apex:toolbar>. The default appearance is green-to-black gradient.
If we are setting in

<apex:toolbar style="background-color:blue"> or any hexadecimal Number it does not works.
In this style sheet we have to include something else too.
<apex:toolbar style="background-color:gray;background-image:none">

The whole example is given below.

<apex:page id="thePage" standardstylesheets="true" showheader="false">

    <apex:toolbar id="theToolbar" height="50px;" itemSeparator="disc" style="background-color:gray;background-image:none">

        <apex:outputText value="Sample Toolbar"/>

        <apex:toolbarGroup itemSeparator="disc" id="toobarGroupLinks">

            <apex:outputLink value="http://www.salesforce.com"><span style="color:Blue">salesforce</span></apex:outputLink>

            <apex:outputLink value="http://developer.salesforce.com"><span style="color:Blue">apex developer network</span></apex:outputLink>

        </apex:toolbarGroup>

        <apex:toolbarGroup itemSeparator="disc" location="right" id="toobarGroupForm">

            <apex:form id="theForm">

                <apex:inputText id="theInputText">Enter Text</apex:inputText>

                <apex:commandLink id="theCommandLink"><span style="color:Blue">Search</span></apex:commandLink>

            </apex:form>

        </apex:toolbarGroup>

    </apex:toolbar>   

</apex:page>

Thanks