[Neftali [Germán.Estévez]]

Te paso una rutinilla que encontré por internet hace tiempo, que aplica un estilo a un richedit cuando el texto ya está.
A ver si te es útil.

Código Delphi [-]
// Resaltar Sintaxis
procedure TFormSQL._ChangeSintaxis(Form:TForm; vStyle:String;
                                     RichE:TRichedit; InVisible:Boolean=True);
const
  // symbols...
  CodeC1: array[0..20] of String = ('#','$','(',')','*',',',
          '.','/',':',';','[',']','{','}','<','>',
          '-','=','+','''','@');
//  // reserved words...
//  CodeC2: array[0..44] of String = ('and','as','begin',
//          'case','char','class','const','downto',
//          'else','end','except','finally','for',
//          'forward','function','if','implementation','interface',
//          'is','nil','or','private','procedure','public','raise',
//          'repeat','string','to','try','type','unit','uses','var',
//          'while','external','stdcall','do','until','array','of',
//          'in','shr','shl','cos','div');

  // reserved words...  SQL
  CodeC2: array[0..209] of String = (
    'ACTION','ADD','ALL', 'ALTER', 'AND', 'ANY', 'AS', 'ASC', 'AUTHORIZATION', 'AVG',
    'BACKUP', 'BEGIN', 'BETWEEN', 'BREAK', 'BROWSE', 'BULK', 'BY',
    'CASCADE', 'CASE', 'CHECK', 'CHECKPOINT', 'CLOSE', 'CLUSTERED', 'COALESCE',
    'COLLATE', 'COLUMN', 'COMMIT', 'COMMITTED', 'COMPUTE', 'CONFIRM', 'CONSTRAINT', 'CONTAINS', 'CONTAINSTABLE', 'CONTINUE', 'CONTROLROW', 'CONVERT', 'COUNT',
    'CREATE', 'CROSS', 'CURRENT', 'CURRENT_DATE', 'CURRENT_TIME', 'CURRENT_TIMESTAMP', 'CURRENT_USER', 'CURSOR',
    'DATABASE', 'DBCC', 'DEALLOCATE', 'DECLARE', 'DEFAULT', 'DELETE', 'DENY', 'DESC', 'DISABLE', 'DISK', 'DISTINCT', 'DISTRIBUTED', 'DOUBLE', 'DROP', 'DUMMY', 'DUMP',
    'ELSE', 'ENABLE', 'END', 'ERRLVL', 'ERROREXIT', 'ESCAPE', 'EXCEPT', 'EXEC', 'EXECUTE', 'EXISTS', 'EXIT',
    'FETCH', 'FILE', 'FILLFACTOR', 'FLOPPY', 'FOR', 'FOREIGN', 'FORWARD_ONLY', 'FREETEXT', 'FREETEXTTABLE', 'FROM', 'FULL', 'FUNCTION',
    'GO', 'GOTO', 'GRANT', 'GROUP',
    'HAVING', 'HOLDLOCK',
    'IDENTITY', 'IDENTITY_INSERT', 'IDENTITYCOL', 'IF', 'IN', 'INDEX', 'INNER', 'INSERT', 'INTERSECT', 'INTO', 'IS', 'ISOLATION',
    'JOIN',
    'KEY', 'KILL',
    'LEFT', 'LEVEL', 'LIKE', 'LINENO', 'LOAD',
    'MIRROREXIT', 'MOVE',
    'NATIONAL', 'NO', 'NOCHECK', 'NONCLUSTERED', 'NOT', 'NOUNLOAD', 'NULL', 'NULLIF',
    'OF', 'OFF', 'OFFSETS', 'ON', 'ONCE', 'ONLY', 'OPEN', 'OPENDATASOURCE', 'OPENQUERY', 'OPENROWSET', 'OPTION', 'OR', 'ORDER', 'OUTER', 'OVER',
    'PERCENT', 'PERM', 'PERMANENT', 'PIPE', 'PLAN', 'PRECISION', 'PREPARE', 'PRIMARY', 'PRINT', 'PRIVILEGES', 'PROC', 'PROCEDURE', 'PROCESSEXIT', 'PUBLIC',
    'RAISERROR', 'READ', 'READTEXT', 'READ_ONLY', 'RECONFIGURE', 'RECOVERY', 'REFERENCES', 'REPEATABLE', 'REPLICATION', 'RESTORE', 'RESTRICT', 'RETURN', 'RETURNS', 'REVOKE', 'RIGHT', 'ROLLBACK', 'ROWCOUNT', 'ROWGUIDCOL', 'RULE',
    'SAVE', 'SCHEMA', 'SELECT', 'SERIALIZABLE', 'SESSION_USER', 'SET', 'SETUSER', 'SHUTDOWN', 'SOME', 'STATISTICS', 'STATS', 'SYSTEM_USER',
    'TABLE', 'TAPE', 'TEMP', 'TEMPORARY', 'TEXTSIZE', 'THEN', 'TO', 'TOP', 'TRAN', 'TRANSACTION', 'TRIGGER', 'TRUNCATE', 'TSEQUAL',
    'UNCOMMITTED', 'UNION', 'UNIQUE', 'UPDATE', 'UPDATETEXT', 'USE', 'USER',
    'VALUES', 'VARYING', 'VIEW',
    'WAITFOR', 'WHEN', 'WHERE', 'WHILE', 'WITH', 'WORK', 'WRITETEXT');

var
  FoundAt : LongInt;
  StartPos, ToEnd, i : integer;
  OldCap,T : String;
  FontC, BackC, C1, C2 ,C3 ,strC, strC1 : TColor;
begin
  OldCap := Form.Caption;
  Self.FStyle := vStyle;
  with RichE do
  begin
//    Font.Name := 'Courier New';
//    Font.Size := 10;
    Font.Name := RichE.Font.Name;
    Font.Size := RichE.Font.Size;

    if InVisible then
    begin
      Visible := False;
      Form.Caption := 'Executing Code Coloring...';
    end;

    if WordWrap then WordWrap := false;
    SelectAll;
    SelAttributes.color := clBlack;
    SelAttributes.Style := [];
    SelStart := 0;

  end;

  BackC := clWhite; FontC := clBlack;
  C1 := clBlack; C2 := clBlack; C3 := clBlack;
  strC := clBlue; strC1 := clSilver;

  if vStyle = 'Twilight' then
  begin
    BackC := clBlack; FontC := clWhite;
    C1 := clLime; C2 := clSilver; C3 := clAqua;
    strC := clYellow; strC1 := clRed;
  end
  else
  if vStyle = 'Default' then
  begin
    BackC := clWhite; FontC := clBlack;
    C1 := clTeal; C2 := clMaroon; C3 := clBlue;
    strC := clMaroon; strC1 := clSilver;
  end
  else
  if vStyle = 'Ocean' then
  begin
    BackC := $00FFFF80; FontC := clBlack;
    C1 := clMaroon; C2 := clBlack; C3 := clBlue;
    strC := clTeal; strC1 := clBlack;
  end
  else
  if vStyle = 'Classic' then
  begin
    BackC := clNavy; FontC := clYellow;
    C1 := clLime; C2 := clSilver; C3 := clWhite;
    strC := clAqua; strC1 := clSilver;
  end
  else
  begin
    with RichE do
    begin
      T := '{'+vStyle+' = Invalid Style [Default,Classic,Twilight,Ocean] ONLY! }';
      Lines.Insert(0,T);
      StartPos := 0;
      ToEnd := Length(Text) - StartPos;
      FoundAt := FindText(T, StartPos, ToEnd, [stWholeWord]);
      SelStart := FoundAt;
      SelLength := Length(T);
      SelAttributes.Color := clRed;
      SelAttributes.Style := [fsBold];
      StartPos := 0;
      ToEnd := Length(Text) - StartPos;
      FoundAt := FindText('ONLY!', StartPos, ToEnd, [stWholeWord]);
      SelStart := FoundAt;
      SelLength := 4;
      SelAttributes.Color := clRed;
      SelAttributes.Style := [fsBold,fsUnderLine];
    end;
  end;

  RichE.SelectAll;
  RichE.color := BackC;
  RichE.SelAttributes.color := FontC;

  for i := 0 to 100 do
  begin
    with RichE do
    begin
      StartPos := 0;
      ToEnd := Length(Text) - StartPos;
      FoundAt := FindText(IntToStr(i), StartPos, ToEnd, [stWholeWord]);
      while (FoundAt <> -1) do
      begin
        SelStart := FoundAt;
        SelLength := Length(IntToStr(i));
        SelAttributes.Color := C1;
        SelAttributes.Style := [];
        StartPos := FoundAt + Length(IntToStr(i));
        FoundAt := FindText(IntToStr(i), StartPos, ToEnd, [stWholeWord]);
      end;
    end;
  end;
  for i := 0 to {20}(Length(CodeC1) - 1) do
  begin
    with RichE do
    begin
      StartPos := 0;
      ToEnd := Length(Text) - StartPos;
      FoundAt := FindText(CodeC1[i], StartPos, ToEnd, []);
      while (FoundAt <> -1) do
      begin
        SelStart := FoundAt;
        SelLength := Length(CodeC1[i]);
        SelAttributes.Color := C2;
        StartPos := FoundAt + Length(CodeC1[i]);
        FoundAt := FindText(CodeC1[i], StartPos, ToEnd, []);
      end;
    end;
  end;
  for i := 0 to {44}(Length(CodeC2) - 1) do
  begin
    with RichE do
    begin
      StartPos := 0;
      ToEnd := Length(Text) - StartPos;
      FoundAt := FindText(CodeC2[i], StartPos, ToEnd, [stWholeWord]);
      while (FoundAt <> -1) do begin
        SelStart := FoundAt;
        SelLength := Length(CodeC2[i]);
        SelAttributes.Color := C3;
        SelAttributes.Style := [fsBold];
        StartPos := FoundAt + Length(CodeC2[i]);
        FoundAt := FindText(CodeC2[i], StartPos, ToEnd, [stWholeWord]);
      end;
    end;
  end;
  Startpos := 0;
  with RichE do
  begin
    FoundAt := FindText('''', StartPos, Length(Text), []);
    while FoundAt <> -1 do
    begin
      SelStart := FoundAt;
      Startpos := FoundAt+1;
      FoundAt := FindText('''', StartPos, Length(Text), []);
      if FoundAt <> -1 then
      begin
        SelLength := (FoundAt - selstart)+1;
        SelAttributes.Style := [];
        SelAttributes.Color := strC;
        StartPos := FoundAt+1;
        FoundAt := FindText('''', StartPos, Length(Text), []);
      end;
    end;
  end;

  Startpos := 0;
  with RichE do
  begin
    FoundAt := FindText('{', StartPos, Length(Text), []);
    while FoundAt <> -1 do
    begin
      SelStart := FoundAt;
      Startpos := FoundAt+1;
      FoundAt := FindText('}', StartPos, Length(Text), []);
      if FoundAt <> -1 then
      begin
        SelLength := (FoundAt - selstart)+1;
        SelAttributes.Style := [];
        SelAttributes.Color := strC1;
        StartPos := FoundAt+1;
        FoundAt := FindText('{', StartPos, Length(Text), []);
      end;
    end;
  end;

  if InVisible then
  begin
    RichE.Visible := True;
    Form.Caption := OldCap;
  end;

  RichE.SelStart := 0;
end;

Los estilos son:
// tipos ('Twilight', 'Default', 'Ocean', 'Classic')

Y para llamada puedes utilizar algo así:

Código Delphi [-]
  _ChangeSintaxis(FormSQL, 'Twilight', RichEdit1);