The underlying Kendo Linear Kendo stopped rendering the track in 2014.3.1314 and, respectively, so does RadLinearGauge as of 2015.1.225

For example, the following snippet should render a wide, green, semi-transparent track, but it does not

			<telerik:RadLinearGauge ID="gauge" runat="server" Height="280">
				<Pointer Value="20">
					<Track Color="#5ca038" Opacity="0.5" Size="30" />
				</Pointer>
			</telerik:RadLinearGauge>