I have three different Donkey Kong Junior cartridges.   #1 is the Atari release with the red label.  This one works great in the original Atari 2600, the Flashback 2 (with cart mod), the Retron 77 (with Stella 6.6), and the new Atari 2600+. #2 is the Coleco release with the white shell.  This one works great in the original Atari 2600, the Flashback 2 (with cart mod), the Retron 77 (with Stella 6.6), and the new Atari 2600+. #3 is another Coleco release with the white shell.