As Simpathey said I would definitely change the squares to have a consistent colour as it's quite difficult to guess the right colour.
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Yeah judging how difficult it will be for others is always hard without play testing, I got so used to the timing of the colour changing I could anticipate when it would transition just before it did and nail the timing, but its super hard for someone who hasn't developed it bases on a lot of the reviews. I definitively will tune the difficulty ramp.