Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

uses
   RichEdit;

 // Underline styles 
const
   CFU_UNDERLINETHICK = 9;
   CFU_UNDERLINEWAVE = 8;
   CFU_UNDERLINEDASHDOTDOT = 7;
   CFU_UNDERLINEDASHDOT = 6;
   CFU_UNDERLINEDASH = 5;
   CFU_UNDERLINEDOTTED = 4;
   CFU_UNDERLINE = 1;
   CFU_UNDERLINENONE = 0;

 procedure RE_SetCharFormat(ARichEdit: TRichEdit; AUnderlineType: Byte; AColor: Word);
 var
   // The CHARFORMAT2 structure contains information about 
  // character formatting in a rich edit control. 
  Format: CHARFORMAT2;
 begin
   FillChar(Format, SizeOf(Format), 0);
   with Format do
   begin
     cbSize := SizeOf(Format);
     dwMask := CFM_UNDERLINETYPE;
     bUnderlineType := AUnderlineType or AColor;
     ARichEdit.Perform(EM_SETCHARFORMAT, SCF_SELECTION, Longint(@Format));
   end;
 end;

 // Underline the current selection with a CFU_UNDERLINEWAVE line style (color red); 
procedure TForm1.Button1Click(Sender: TObject);
 begin
   RE_SetCharFormat(RichEdit1, CFU_UNDERLINEWAVE, $50);
 end;