You could handle the DrawCell event, and do all the drawing yourself. This would mean filling the background and drawing the text. If you only have TextBox cells, then this would not be a lot of work as you can use the GridStaticCellRenderer.DrawText method to manage the drawing of the text for you. But if you have several different CellTypes, then this may become cumbersome.
Another solution not exactly what you have now, but maybe close enough, woul dbe to handle teh CellDrawn. There is e.RowIndex points to one of your special colored cells, you could just fill a rectangle over the cell will a mostly transparent color using alphablending. This would work not matter what the cell type was. Here is a sample handler to give you the idea.
private void gridControl1_CellDrawn(object sender, Syncfusion.Windows.Forms.Grid.GridDrawCellEventArgs e)
{
if(e.RowIndex == 2 && e.ColIndex > 0)
{
using(Brush br = new SolidBrush(Color.FromArgb(60, Color.Orange)))
{
e.Graphics.FillRectangle(br, e.Bounds);
}
}
else if(e.RowIndex == 5 && e.ColIndex > 0)
{
using(Brush br = new SolidBrush(Color.FromArgb(60, Color.Blue)))
{
e.Graphics.FillRectangle(br, e.Bounds);
}
}
}