Because the demand is niche, the best are the ones you make yourself using tools like GIMP (free) or Photoshop.
Keep it small (under 60KB) to ensure smooth loading via the CPS (Customer Programming Software). How to Change Your Background Image anytone background images
Use Coolors.co to generate a 5-color palette. For an Anytone aesthetic, choose colors that are analogous (neighbors on the color wheel) rather than complementary (opposites). Analogous colors blend better across different screen brightnesses. Because the demand is niche, the best are