In the Monkey Island 2 demo, Jojo has a completely different appearance, looking more like the monkey from The Secret of Monkey Island. His inventory icon uses his final design, though.
Ok, so the developers just used the monkey from the first game as a placeholder, right? It's possible, but I think there might be something more interesting going on.
The grey monkey in MI1 may have actually been called Jojo during development as well. He ended up unnamed in the final game, but the name seems to still be present in the source files.
So, given there's evidence of both monkeys sharing the same name and the same look at one point, I think it's very likely that this was literally intended to be the same monkey from the first game at some point during development. The developers probably dropped the idea when they gave MI2 Jojo a new design, but the name stuck.
Normally, Guybrush will refuse to exit from the kitchen into the bar, because he doesn't want to get caught by the barkeeper.
However, this is only the case after Guybrush has already been in the bar at least once! If he's never been in the bar, then Guybrush will go through, only to get immediately told off by the barkeeper.
There's a special trick used in the bar to make Guybrush appear darker when he's on the right side of the screen, as if he's in shadow. The game does this by changing the brightness of certain colors in the room's color palette.
Unfortunately, the piano happens to share two of Guybrush's colors. This means that certain pixels on the piano also become brighter or darker depending on where in the room Guybrush is standing.
