Even though you guys didnt get to finish this, what you made is still a pretty cool sandbox. The paint gun reminds me of portal's gel mechanics, and I think it could make for some solid platforming.
I had a lot of fun just running around the cave and getting to the end of it and then going back.
On the aspect of metroidvania, since you have different paints, those could be unlockables that you could get as a reward for exploring or completing things, and the new paints would allow the player to explore more. This seems like the idea you guys were going for, and if it is, I really like it. I normally don't like the idea of a 3d metroidvania, but this setup seems really cool to me.