When Keith rides the tunnel to the Green Lion, the background around him shows stone seen in the tunnel for the Black Lion, instead of the roots and branches surrounding the Green Lion - footage wasn't changed from any other scene of him traveling to fly.
When the team goes to the lions for the first time Keith is running towards #1, when he was actually in the Green Lion. Also in one of the running scenes the Black Lion is shown, when that is the missing key.
After the Black and Yellow Lions go toppling in the final scene, an interior split-screen shows Keith flipping, but on the other side is Sven rather than Hunk - though Sven's Blue Lion is not knocked aside until a moment later after all others have stopped (he is shown again being knocked straight backward in it).
The five lights making up the star around the main light in the Lion Keith was taking off in flashed blue rather than white, but this is because it's the Green instead of the Black Lion.