[]
Gets or sets the ThemeColor value applied to the outer and inside borders in the collection.
Use this property to apply a workbook theme color instead of a fixed Color. If the borders do not use a theme color, this property returns None. To set a diagonal border, use this[BordersIndex] with DiagonalDown or DiagonalUp.
ThemeColor ThemeColor { get; set; }
Property ThemeColor As ThemeColor
IBorders borders = worksheet.Range["B2:E6"].Borders;
borders.LineStyle = BorderLineStyle.DashDot;
borders.ThemeColor = ThemeColor.Accent2;
ThemeColor themeColor = borders.ThemeColor;