How do I change the puzzle background color in the game UI?
Background color helps you separate pieces from the table — not for looks. Start dark so light pieces stand out; later switch closer to the image so details are easier to tell apart. No single color works for a whole game; change it when you cannot see clearly.
Early on: use a dark color
At the start pieces are scattered. Find the edges and big color areas first. A dark gray or black background makes light pieces stand out and edges easier to align.
Later: move closer to the image colors
In the second half, remaining pieces often look very similar. If the background is too bright or too dark, you only see outer outlines and miss that bit of green or brown inside.
Then switch the background to a color already in the image, a little darker. Lots of leaves? Use deep brown so greens pop. Lots of soil? Use deep green so earth tones stand out.
Cannot see clearly? Switch
No color fits an entire game. Dark early for edges; closer to the image later. If the background is in the way, change it — faster than staring at the same piece.