[NumLock]

так и делай в WM_CTLCOLORSTATIC:

Код:

function WindowProc(hwnd: HWND; uMsg: UINT;
  wParam: WPARAM; lParam: LPARAM): Longint; stdcall;
begin
  case uMsg of
    WM_CTLCOLORSTATIC: begin
      SetBkColor(wParam, $ffffff);
      SetTextColor(wParam, $000000);
      Result:=GetStockObject(WHITE_BRUSH);
      Exit;
    end;

черный текст на белом фоне