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Gets or sets the theme color of this gradient stop.
Use this property to read the theme color of a gradient stop, or to apply a workbook theme color to a gradient stop. If the gradient stop does not use a theme color, this property returns None.
ThemeColor ThemeColor { get; set; }
Property ThemeColor As ThemeColor
IRange range = worksheet.Range["A1"];
range.Interior.Pattern = Pattern.LinearGradient;
IColorStop colorStop = ((ILinearGradient) range.Interior.Gradient).ColorStops[0];
colorStop.ThemeColor = ThemeColor.Accent1;
ThemeColor themeColor = colorStop.ThemeColor;