Interesting that you haven't had any luck with Blue. I thought it's the easiest to win with, since you're taking no damage at all, and grind enemies down with Retaliate. You gotta pick your fights though cause enemies that like to set up will end it. I didn't play a lot since the introduction of unlocks however, so it's possible that the Spade symbol is what made it easy, and that being locked now made Blue that much worse.
Bones I think aren't too bad if you get a Power build. They're worse than Fist at the start, but they even out at +1 Power and become better at +2.
The Malfunction boss is meant to be countered by having a large quantity of symbols. Might be too strong however, probably shouldn't give 2 symbols per turn right away.
Avocado is pure green, the core is brown which is not a symbol color. Might make it black or gray to reduce the risk of confusion.
Color-blind mode is absolutely necessary for full release and will be implemented... Somehow. I have no idea how this is going to play out in practice. Reels fly by fast so glance value is important, I don't know if extra symbols or frames will be clear enough unless I slow down the reels. It'll be a headache to implement for sure
To make the game easier to understand, I think just explicitly telling the player in a tutorial that reel timing matters should be enough. I could even do a hand-holdy tutorial that won't progress until the timing is perfect, but I don't like those.