자마린 스튜디오 RGB Slider 컨트롤 데모 입니다.

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="DemoSlider.RGBSlider">
    <ContentPage.Padding>
        <OnPlatform x:TypeArguments="Thickness"
            iOS="10, 20, 10, 10"
            Android="10, 0, 10, 10"
            WinPhone="10, 0, 10, 10" />
    </ContentPage.Padding>
 <StackLayout>
     <StackLayout.Resources>
         <ResourceDictionary>
             <Style TargetType="Slider">
                 <Setter Property="Maximum" Value="255" />
             </Style>
             <Style TargetType="Label">
                 <Setter Property="FontSize" Value="Large" />
                 <Setter Property="HorizontalTextAlignment" Value="Center" />
             </Style>
         </ResourceDictionary>
     </StackLayout.Resources>
     <Slider x:Name="redSlider"
         ValueChanged="OnSliderValueChanged" />
        <Label x:Name="redLabel" />
        <Label x:Name="greenLabel" />
        <Label x:Name="blueLabel" />

        <Slider x:Name="greenSlider"
             ValueChanged="OnSliderValueChanged" />
         <Slider x:Name="blueSlider"
             ValueChanged="OnSliderValueChanged" />
         <BoxView x:Name="boxView"
             VerticalOptions="FillAndExpand" />
     </StackLayout>        
    
</ContentPage>



using System;
using System.Collections.Generic;

using Xamarin.Forms;

namespace DemoSlider
{
    public partial class RGBSlider : ContentPage
    {
        public RGBSlider()
        {
            InitializeComponent();

            redSlider.Value = 128;
            greenSlider.Value = 128;
            blueSlider.Value = 128; 
        }

        void OnSliderValueChanged(object sender, ValueChangedEventArgs args)
        {
            if (sender == redSlider)
            {
                redLabel.Text = String.Format("Red = {0:X2}", (int)redSlider.Value);
            }
            else if (sender == greenSlider)
            {
                greenLabel.Text = String.Format("Green = {0:X2}", (int)greenSlider.Value);
            }
            else if (sender == blueSlider)
            {
                blueLabel.Text = String.Format("Blue = {0:X2}", (int)blueSlider.Value);
            }

            boxView.Color = Color.FromRgb((int)redSlider.Value,
            (int)greenSlider.Value,
           (int)blueSlider.Value);
        }
    }
}