In data grid view course wise set fore & Back color

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C#

int value = Datagridviewcourse.Columns["Course"].Index;
           {
               if (value == 2)
               {
                   e.CellStyle.BackColor = Color.Plum;
                   e.CellStyle.ForeColor = Color.Red;
               }
           }

when i run for data grid view fore and back color as red and plum.
in the data base different course are there.

int value1 = Datagridviewcourse.rows["REO"].index
{
  if (value1 == 2)
  {
      e.CellStyle.BackColor = Color.blue;
      e.CellStyle.ForeColor = Color.black;
  }
}

when i run show the error as follows;

The best overloaded method match for   'System.Windows.Forms.DataGridViewRowCollection.this[int]' has some invalid arguments


Argument '1': cannot convert from 'string' to 'int'

the above two error shows in

 int value1 = Datagridviewcourse.rows["REO"].index(this line)

what i am doing is in database different course are there.in all course there are some 3 to 5 entries in datagridview.based on the course in data grid view i assign for particular fore and Back color in data grid view.

for that only i written the above code.

from my what is the mistake.
help me.