procedure TForm1.Edit1Change(Sender: TObject);
begin
If (Sender as TEdit).Text = '' then begin
(Sender as TEdit).Color := clDefault;
Exit;
end;
with ZQuery1 do begin
// SQL.Clear; // you don't need this if you directly set SQL.Text property
SQL.Text := 'SELECT * FROM baza WHERE Nazwisko LIKE :Nazwisko'; // If you use ZEOSdbo you don't need Active := False at beginning
// Active := False; // don't need this here
ParamByName('Nazwisko').AsString := (Sender as TEdit).Text + '%';
// Active := False; // don't need this here
Open;
If Eof then (Sender as TEdit).Color := clRed
else (Sender as TEdit).Color := clGreen;
end;
end;