Day and Night mode

The day and night mode is a cosmetic feature in which when the player reaches 700 points the game begins to switch between day (white background, black lines and shapes) and night (black background, white lines and shapes). Reaching a score of 900 will switch the color scheme back to day, and the switch back and forth will occur at further subsequent milestones.

Pattern
It appears that at every 700 points, a night cycle will last for 200 points, though this may require more testing.