If you have the need to change the row color of a row in a gridview when you mouse over (and mouse out) you can add some code to the RowDataBound event.
Here is a sample:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
//Only apply to data rows
if (e.Row.RowType == DataControlRowType.DataRow)
//Add mouse over event to change row background color
//Add mouse out event to change row background color back to white
Here is the blog site where I found this sample.