iGrid provides you with several settings related to selection. Does your grid work in row mode? Do you use multi-selection? Do you need to change the background color of all cells in a row or are we talking about changing the color of selection? In the first case, you can use iGRow.Cells.BackColor property. In the second case use the properties of iGrid related to selection, such as SelCellsBackColor and SelRowsBackColor.
In any case it would be nice to see an example demonstrating what you are doing. Read also the comprehensive Cell Selection and Current Cell section in the documentation to understand how you can control selection in iGrid.