Code:

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;