You can do this:
dataGridView1.SelectedCells[0].Style
= new DataGridViewCellStyle { ForeColor = Color.Yellow};
You can also set whatever style settings (font, for example) in that cell style constructor.
And if you want to set a particular column text color you could do:
dataGridView1.Columns[colName].DefaultCellStyle.ForeColor = Color.Yellow;
dataGridView1.Columns[0].DefaultCellStyle.BackColor = Color.Blue;
updated
So if you want to color based on having a value in the cell, something like this will do the trick:
private void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
if (dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value != null && !string.IsNullOrWhiteSpace(dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value.ToString()))
{
dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Style = new DataGridViewCellStyle { ForeColor = Color.Orange, BackColor = Color.Blue };
}
else
{
dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Style = dataGridView1.DefaultCellStyle;
}
}