Loop through the rows of the datagrid, and basaed on your conditions change the color.
For e.g.
for(int i = 0; i<dgvReservations.RowCount; i++)
{
if (myGird.Rows[i].Cells[conditionCell] == myCondition);
{
myGrid.Rows[i].DefaultCellStyle.BackColor = System.Drawing.Color.Red;
}
}