Try TitleStyle
Example
<GridLayout>
<RadRadialGauge title="7H">
<TitleStyle tkRadialGaugeTitleStyle textColor="red" textSize="20"></TitleStyle>
<RadialScale tkRadialGaugeScales startAngle="0" sweepAngle="360" minimum="0" maximum="100" radius="0.9">
<ScaleStyle tkRadialScaleStyle ticksVisible="false" labelsVisible="false" lineThickness="0"></ScaleStyle>
<RadialBarIndicator tkRadialScaleIndicators minimum="0" maximum="100" location="0.5">
<BarIndicatorStyle tkRadialBarIndicatorStyle fillColor="rgba(224,151,36,0.5)" barWidth="0.2"></BarIndicatorStyle>
</RadialBarIndicator>
<RadialBarIndicator tkRadialScaleIndicators minimum="0" maximum="0" location="0.5" isAnimated="true">
<BarIndicatorStyle tkRadialBarIndicatorStyle cap="Round" fillColor="rgba(224,151,36,1)" barWidth="0.2"></BarIndicatorStyle>
</RadialBarIndicator>
</RadialScale>
</RadRadialGauge>
</GridLayout>