For the time being the following workaround can be used:

CSS:

    <style>
     .RadButton.RadButton_Metro.rbSkinnedButton:focus input.rbDecorated {
            background-color: #25A0DA !important;
        }
    </style>

        <telerik:RadSkinManager ID="RadSkinManager1" runat="server" Skin="Metro"></telerik:RadSkinManager>
        <telerik:RadTextBox ID="RadTextBox1" runat="server"></telerik:RadTextBox>
        <telerik:RadButton ID="RadButton1" runat="server" Text="click" />