Definitely a fun idea!

I think the game would improve if it were a little slower, or if at least it started slow and then ramped up. I basically never had any time to react to the color of a cube, much less attempt to place it somewhere, and if I did manage to do it for one paddle, I certainly didn't manage it for the other. I think slowing the game down would do a lot to mitigate that. I'm not sure still how much control one really has over where something goes. The paddles really only seem good at changing whether something is moving vertically, when this game's mechanics are more concerned with where something is horizontally. Maybe if there were only one paddle and you could move the paddle around in addition to just flopping it back and forth?

Anyway, after I gave up on controlling the cubes, I just let the game alone and watched the cubes fall where they may. It makes for a nice screensaver.

Spawn rate is way too fast to let us take a decision, but liked the idea.

Really cool idea! I didn't feel like I had very much control over the outcome though because everything was moving so quickly and bounces were really hard to read. I would maybe start by making the play area smaller and slow down the boxes movement a little bit (maybe mess with the gravity?), I think that would give some more player choice. I think the concept of mixing the chemicals combined with the stacking was really cool though, well done!

I liked the interactions of the boxes, it felt like a chemistry kinda sim for sure. Would've been cool if there were more colors that resulted in fires, explosions etc.
I also didn't feel like I had much control over my tower so I couldn't really try and make it efficiently just hope that it would work out.
The concept is really good and it worked really well!