The significant properties unique to RadColorDialog are:

ActiveMode: Determines the currently selected tab.  Valid enumeration values from Telerik.WinControls.ColorPickerActiveMode are Basic, System, Web, Professional.

AllowColorPickFromScreen: When true (the default) the "eye dropper" tool is displayed.

AllowColorSaving: Toggles the "Add a custom color" button visibility.

BackColor: The background color of the color selector as a whole. You can also set this color to be Transparent to have it blend in with your other UI elements.

ForeColor: The color for labels and text entry.

SelectedColor: In the figure below the SelectedColor is labeled as "New".

OldColor: In the figure below the OldColor is labeled as "Current".

ShowBasicColors, ShowSystemColors, ShowWebColors, ShowProfessionalColors: If true (the default) the corresponding Basic, System, Web and Professional tabs are displayed.

AllowEditHEXValue: If true (the default) enables hexadecimal entry of color values.

ShowHEXColorValue: If true (the default) displays the hexadecimal entry of color values.

CustomColors[]: This is a read-only array of Color objects.  You can query the contents of the custom colors displayed along the bottom of the selector.

Copy[C#] Enlist the current custom colors in RadColorDialog

private void radButton1_Click(object sender, EventArgs e)
{
    StringBuilder sb = new StringBuilder();
    foreach (Color color in radColorDialog1.CustomColors)
    {
        sb.Append(color.ToString());
        sb.Append(System.Environment.NewLine);
    }
    MessageBox.Show(sb.ToString());

}

Copy[VB.NET] Enlist the current custom colors in RadColorDialog

Private Sub RadButton1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadButton1.Click
    Dim sb As New StringBuilder()
    For Each color As Color In RadColorDialog1.CustomColors
        sb.Append(color.ToString())
        sb.Append(System.Environment.NewLine)
    Next
    MessageBox.Show(sb.ToString())
End Sub

Localization/Internationalization Properties:  The text values of the RadColorDialog can be customized for easy localization including properties AddNewColorButtonText, BasicTabHeading, SystemTabHeading, WebTabHeading, ProfessionalTabHeading, SelectedColorLabelHeading and OldColorLabelHeading.

In order go get the SelectedColor or the SelectedHlsColor you can use the following code snippet:

Copy[C#] Enlist the current custom colors in RadColorDialog

if (radColorDialog1.ShowDialog() == DialogResult.OK)
{
    Color color = radColorDialog1.SelectedColor;
    HslColor hslColor = radColorDialog1.SelectedHslColor;
}

Copy[VB.NET] Enlist the current custom colors in RadColorDialog

If RadColorDialog1.ShowDialog() = DialogResult.OK Then
    Dim color As Color = RadColorDialog1.SelectedColor
    Dim hslColor As Telerik.WinControls.HslColor = RadColorDialog1.SelectedHslColor
End If