[ecfisa]

Hola ToritoCapo.

Probá este código:

void __fastcall TForm1::DBGrid1DrawColumnCell(TObject *Sender,
      const TRect &Rect, int DataCol, TColumn *Column, TGridDrawState State)
{
  if(DBGrid1->DataSource->DataSet->FieldByName("STOCK_ACTUAL")->Value <
     DBGrid1->DataSource->DataSet->FieldByName("STOCK_CRITICO")->Value) {
    DBGrid1->Canvas->Brush->Color = clRed;
    DBGrid1->Canvas->Font->Color = clWhite;
    DBGrid1->DefaultDrawColumnCell(Rect, DataCol, Column, State);
  };
}

Un saludo.