Use the CellFormatting
event of the DataGridView
dgv.CellFormatting += dgv_CellFormatting
Handle it like
void dgv_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
if(dgv.Rows[e.RowIndex].Cells["fullPath"].Value.ToString().Equals("none"))
dgv.Rows[e.RowIndex].DefaultCellStyle.ForeColor = Color.Red;
else
dgv.Rows[e.RowIndex].DefaultCellStyle.ForeColor = Color.Black;
}