hsr///////////////////////////////////////////////////////////
다른 방법도 있겠지만 일단 찾아서 선택으로 놓고 색을 바꿔봤습니다
procedure TForm1.Button1Click(Sender: TObject);
var
    StartPos, str_Length, FoundAt: Integer;
    str:string;
begin
    RichEdit1.Lines.Add('넓고푸른바다' );
    RichEdit1.SelStart := 0;
    str := '푸른';

    repeat
       StartPos := RichEdit1.SelStart;
       str_Length := Length(RichEdit1.Text) - StartPos;
       FoundAt := RichEdit1.FindText(str, StartPos, str_Length, [stMatchCase]);
       if FoundAt <> -1 then begin
          SetFocus;
          RichEdit1.SelStart := FoundAt;
          RichEdit1.SelLength := Length(str);
          RichEdit1.SelAttributes.Color := clBlue;
          RichEdit1.SelStart := RichEdit1.SelStart + RichEdit1.SelLength;
       end;
    until FoundAt < 0;
end;