Thank you for playing and sharing your thoughts! We tried a lot of variations to balance the sleek two-color visuals we were going for with sufficient distinctiveness for the puzzle, and I'm sorry to hear we fell on the wrong side of that for you. I do like the idea of highlighting only available icons - but the issue we found there was that, since you can match from both endpoints, essentially half the board would be highlighted. It ended up being too much visual info rather than helpful, in my opinion anyway.
These things are always a judgment call, so it's always helpful to hear feedback -thank you!