I think to improve it, when 3 of the different colored mushrooms are put in the same cauldron it should not just get stuck and just do nothing, and no longer be usable, I don't like this :(.
Also, I think for it to be more accessible such as to people who may fully or partially color blind, if you have major elements of the game dependent on recognizing colors, I think it's important there are also distinct symbols or patterns inside these elements somewhere so that people can easily tell these apart by other ways than just color.
That includes after it's put into the cauldron as well, which is just three circles above the cauldron currently in your game, that change to a solid color based on what color mushroom you put into the cauldron.
Because color is so particularly important as a mechanic in your game, I think it may be important to make it more accessible in this specific way for yours so more people could be able to play it.
It is also beneficial to do this for all players so things are very distinct and easy to tell apart.
Finally, something about the game, even with the in-depth tutorial there, seemed like it would be difficult for a newer or inexperienced player to games in general, more so than some other games.
I could imagine they may not figure it out and just simply give up and close the game.
But, this may have been heavily influenced by the fact that the 3 non matching colors in a cauldron just make the cauldron get stuck and do nothing and no longer be usable - with no visual, auditory, or any other indicator how or why this happened. I am guessing this may not be the way you intended and might even potentially be a bug, but I'm not sure about it.
When this happens and a cauldron becomes unusable, it's just better to start the game over from the beginning, and try again.
I think what it should do is reset it after 3 mushrooms are put in that were not matching colors (with some sort of cue ideally, but at the least, just make all the slots available again and give no benefit or gain to the player).
However even with these things above I really loved the gorgeous visuals and clean mechanic, I thought it was very fun and interesting.
I really liked this idea, and this game overall a lot, and I think you did a really great job on this game!