Excel.Style style = Globals.ThisWorkbook.Styles.Add("NewStyle", missing);
style.Interior.Color = System.Drawing.ColorTranslator.ToOle(System.Drawing.Color.White);
style.Interior.Pattern = Excel.XlPattern.xlPatternSolid;
Microsoft.Office.Tools.Excel.NamedRange rangeStyles = this.Controls.AddNamedRange(this.Range["A1", missing], "rangeStyles");
rangeStyles.Style = "NewStyle";
rangeStyles.Columns.AutoFit();
Using C# code to change the background color of an Excel spreadsheet range[
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try below
.net - Change the background of Cells with C# - Stack Overflow[
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