Auto save per level might be there and I just didn't notice, but I was thinking more in regards to the save function and how it works.
As for the limited colour... what I think would be interesting then is to make open spaces black instead of white. That way, the player can quickly recognize that white = solid while black = empty.
For the "bugs," hopefully the VOD will make these more clear. However, to summarize them... I found I couldn't exit the tutorial level unless I jumped first. I otherwise got caught on something. For the weird line, I noticed this at some point later in my playthrough but I would see a black vertical line that sat ABOVE the cross that acts as the player's targeting reticle. And for the third one, the second stage has platforms that shoot the player in a direction indicated by an arrow on them. However, the arrows looked slightly off. This one in particular should be more clear with the VOD, which will likely take me another few days to get up (I'm getting my first VODs set up now and setting up release days).
Finally, there are 3D games that have these platforms too. In fact, the first thing that comes to mind is another Mario game: Super Mario 3D Land and Super Mario 3D World!