Read Excel cell Background-Color  from Excel Sheet using  open Xml SDK        

  

//Read background color and fill the pattern

  DocumentFormat.OpenXml.Spreadsheet.PatternFill pf = GetCellPatternFill(cell, doc);

 DocumentFormat.OpenXml.Spreadsheet.ColorType ct= pf.ForegroundColor;

   
 string backgroundcolor=ct.Rgb.Value;              

--------------------------------------------------------------------------------------------------------------------

public static DocumentFormat.OpenXml.Spreadsheet.PatternFill GetCellPatternFill(Cell theCell, SpreadsheetDocument document)
        {
            WorkbookStylesPart styles = SpreadsheetReader.GetWorkbookStyles(document);


            int cellStyleIndex;
            if (theCell.StyleIndex == null) // I think (from testing) if the StyleIndex is null
           {                               // then this means use cell style index 0.
                cellStyleIndex = 0;           // However I did not found it in the open xml
            }                               // specification.
            else
            {
                cellStyleIndex = (int)theCell.StyleIndex.Value;
            }

            CellFormat cellFormat = (CellFormat)styles.Stylesheet.CellFormats.ChildElements[cellStyleIndex];

            DocumentFormat.OpenXml.Spreadsheet.Fill fill = (DocumentFormat.OpenXml.Spreadsheet.Fill)styles.Stylesheet.Fills.ChildElements[(int)cellFormat.FillId.Value];
            return fill.PatternFill;
        }