You can try to use script working with

using System.Runtime.InteropServices;
using Microsoft.Office.Interop.Excel;

Method looks like this:

public void FormatColor(Worksheet ThisSheet, String cell1)
{
    Range rg = ThisSheet.get_Range(cell1, System.Type.Missing);
    //rg.Font.Color = System.Drawing.ColorTranslator.ToOle(System.Drawing.Color.Red); //this sets font color
    rg.Interior.Color = System.Drawing.ColorTranslator.ToOle(System.Drawing.Color.Red);

    Marshal.FinalReleaseComObject(rg);
}

Then, in automation you can use it like this:

2:2 here selects entire second row.

A:A would select entire column A.

B2:C3 would select 4 cells starting from B2 till C3.