I love this!! This is such a brilliant idea. It definitely took some learning (a tutorial would have been nice) but once I got it, I really enjoyed it. Finding combos was really cool i.e. place red and green, and suddenly you're blasting away enemies. The purple was an awesome touch - I loved diving through enemies' trails and setting up a new location on the other side to shoot from. I thought the game could've benefited from combining some colours? Maybe red could be faster movement and faster shooting - 3 colours might be a bit more manageable. Overall, brilliant idea, fantastic first game jam, can't wait to see what you make next! 5 star creativity from me.
A gamejam specific point: Godot can export to HTML5 - definitely do it! Lots more people will play your game because they don't feel comfortable downloading files which might be harmful. I used this guide (https://foosel.net/til/how-to-export-a-godot-4-game-to-run-on-the-web-on-itchio/).