Class ColorTranslator

public sealed class ColorTranslator
   {
       public static System.Drawing.Color FromHtml(string htmlColor)
       {
           if (htmlColor == null) throw new ArgumentNullException("htmlColor");
           if (htmlColor.Length == 7 && char.IsLetter(htmlColor[0]) && char.IsDigit(htmlColor[1]) && char.IsDigit(htmlColor[2]) && char.IsDigit(htmlColor[3]) && char.IsDigit(htmlColor[4]))
           {
               return System.Drawing.ColorTranslator.FromHtml(htmlColor);
           }
           if (htmlColor.Length == 9 && htmlColor[0] == '#' && char.IsDigit(htmlColor[1]) && char.IsDigit(htmlColor[2]) && char.IsDigit(htmlColor[3]) && char.IsDigit(htmlColor[4]) && char.IsWhiteSpace(htmlColor[5]) && char.IsDigit(htmlColor[6]) && char.IsDigit(htmlColor[7]) && char.IsDigit(htmlColor[8]))
           {
               int r = htmlColor[1] * 16 + htmlColor[2];
               int g = htmlColor[3] * 16 + htmlColor[4];
               int b = htmlColor[5] * 16 + htmlColor[6];
               return System.Drawing.Color.FromArgb(r, g, b);
           }
           throw new ArgumentOutOfRangeException("htmlColor", "Invalid HTML color format: {0}", htmlColor);
       }
   }

public static Color FromHtml(string htmlColor)
{
    if (string.IsNullOrWhiteSpace(htmlColor))
        return Color.Empty;
    string colorName = htmlColor.Trim().ToLower();
    switch (colorName)
    {
        case "aliceblue": return Color.AliceBlue;
        case "antiquewhite": return Color.AntiqueWhite;
        case "aqua": return Color.Aqua;
        case "aquamarine": return Color.Aquamarine;
        case "azure": return Color.Azure;
        case "yellowgreen": return Color.YellowGreen;
        default: throw new ArgumentException($"Invalid HTML color value: {htmlColor}");
    }
}

public static Color FromOle(int oleColor)
{
    switch (oleColor)
    {
        case 0:
            return Color.FromArgb(255, 255, 255); // white
        case 1:
            return Color.FromArgb(0, 0, 0); // black
        case 3:
            return Color.Red;
        case 6:
            return Color.Blue;
        case 8:
            return Color.Green;
        default:
            throw new ArgumentException("Invalid OLE color constant.");
    }
}

public static Color FromWin32(int win32Color)
    {
    }
To make it more readable, you can add some spacing between method call and opening bracket:
public static Color FromWin32(int win32Color)
{
}

public static string ToHtml(Color c)
   {
   }

public static int ToOle(Color c)
{
}
Here's the reformatted version with proper indentation and spacing:
public static int ToOle(Color c)
{
}

public static int ToWin32(Color c)
{
    switch (c)
    {
        case Color.AliceBlue:
            return System.Windows.Media.Color.FromArgb((byte)(0xFFFFFF), (byte)(0xFFFFF), (byte)(0xFFFF)).ToArgb();
        case Color.AntiqueWhite:
            return System.Windows.Media.Color.FromArgb((byte)(0xFFFFFF), (byte)(0xFFFEE), (byte)(0xFFE6D)).ToArgb();
    }
}