ok i can confirm its some other issue than my scene, I was just playing some games in scira arcade and same happened. that is game has different graphics and suddenly every object is swapped with that gradient (even text box).
Though is weird must still be in combo with something, I played irrational fear of unicorns and Air Space a lot without this glitch and your-first-step game got that glitch twice while playing.
suddenly all game objects just take gradient appearance like that in image. could not yet trace exactly when it happens