Apollo 13 wasn't the only more than 6 ball machine, IJ4 has 8 ball multiball.
If we're just doing SS / DMD era machines, I think the first colored legs and only colored legs before the LE stuff was Road Show, which had the blue legs. I might be wrong about that, but I can't think of anything else.
For first "Ambient (non-topper) light", I'm not sure exactly what you're looking for, but JP has lights and flashers on top of the head which simulate lightning. Unlike a machine like, say, Pinbot where the topper needs to be there for the lights to be there, JP has these built in and they will flash regardless of any topper being there. It looks awesome if you're playing in a dark, tall room. I'm not certain it was the first, but I believe it was.
For use of magnetic ramp or lane diverter, I feel like this was WCS94 with the ball lock. It has been used pretty sparingly in history, with the majority of it's uses on John P's machines, and that was the first one. Anyone know of anything differently?
First motorized target bank is PinBot, I believe. At least, in the way that we think of target banks in the "modern" era.
For first hinged backbox, I'm not positive, but this may have started with High Speed. I'm all but certain it was Williams who did it. High Speed is also (I stole this from the IPDB... the first pinball to play a complete song, first use of Auto Percentaging (for replay scores), first Jackpot available only during multiball, first use of broken switch compensation programming, first SS game with operator report, and the first use of credit dot (malfunction indicator).
And whomever suggested that Humpty Dumpty didn't have flippers but had bumpers that moved, no - it definitely had flippers. In fact, I own three or four machines that are before 1950 that all have flippers on them. Generally, they pivot on the opposite side to what we expect today, but they are the same as flippers.