uses Winapi.RichEdit;

procedure RE_SetSelBgColor(RichEdit: TRichEdit; AColor: TColor);
var
 Format: CHARFORMAT2;
begin
 FillChar(Format, SizeOf(Format), 0);

 with Format do            begin
   cbSize := SizeOf(Format);
   dwMask := CFM_BACKCOLOR;
   crBackColor := AColor;
   Richedit.Perform(EM_SETCHARFORMAT, SCF_SELECTION, Longint(@Format));
 end;

end;

procedure TMainForm.ToolButton14Click(Sender: TObject);
begin
   RE_SetSelBgColor(editor, clYellow);   //设置 文字 背景色
   editor.SelLength:=0;
end;