😂 Thanks so much for playing, and so happy you enjoyed the game!
For your question -- you may notice there's box "drops" that drop onto your bar as you progress. The gray ones make part of the bar obscured for a small time so it's harder to see (as you progress the amount that it covers increases). It's intended to make you rely less on visuals to time your presses.
p.s. 9000 score is amazing! My highest is 7550, and that was hard to get. Nice job!