<input:RadEntry Text="Hello" TextColor="Red" />

private void Button_Clicked(object sender, System.EventArgs e)
        {
            this.radEntry.Text = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. ";
        }

<OnPlatform x:TypeArguments="x:String" x:Key="BoldFont">
    <On Platform="Android" Value="OpenSans-Bold.ttf#Open Sans" />
    <On Platform="iOS" Value="OpenSans-Bold" />
 </OnPlatform>

    <Style x:Key="LoginEntryStyle"
           TargetType="telerikInput:RadEntry">
        <Setter Property="TextColor"
                Value="{StaticResource DarkTextColor}" />
        <Setter Property="WatermarkTextColor"
                Value="{StaticResource LightBlueColor}" />
        <Setter Property="FontSize"
                Value="14" />
        <Setter Property="FontFamily"
                Value="{StaticResource BoldFont}" />
        <Setter Property="HeightRequest"
                Value="48" />
        <Setter Property="Margin"
                Value="0,0,0,16" />
        <Setter Property="BorderStyle">
            <Setter.Value>
                <telerikInput:BorderStyle BorderColor="{StaticResource LightBlueColor}"
                                          BorderThickness="1"
                                          CornerRadius="8" />
            </Setter.Value>
        </Setter>
    </Style>