Thank you so much for your in-depth feedback! This kind of feedback is what helps me grow, and I can tell a lot of time went into it. I appreciate it.
My colors are - surprisingly - mostly random. I have turned on that new tracks automatically get assigned a new color (in Settings > View > Tracks > Track Color: Auto-assign-24 Colors). Sometimes I customize a color myself. It also really helps if you select multiple tracks simultaneously; if you then choose 'Right-click > Region Colors' in the Piano-roll Editor, you can see and distinguish different tracks with their own respective colors. My idea is that similar instruments get a similar color, but my colors tend to be a bit random still haha.
Oh wow, I love the idea of instruments matching colors! That is such a cool way of thinking about them. I definitely do not do this intentional using colors - but I do think of instruments in terms of how 'snappy' (sharp vs round), 'peaceful', etc. they are. I have added weird instruments in the past a lot - a theremin in an underwater song, a timbales in a horror-song, a guitar and flute in nearly any song... One of the thing I like most is experimenting and finding a new set of instruments or chords that work well!
Thanks again for commenting! Looking back, I do say I have improved a lot. I keep track of my rank and score for each of the music jams and keep them in an Excel file, so I can visualize this upward trend. Given my nature to explore wild new ideas (like 9/8 time signatures, Lydian modes, changing rhythms...), my songs will not always end up working out, but that's okay. I am enjoying this a lot, and that's what counts! And comments from people like you are what I maybe enjoy the most :)