Ton van Overbeek
Ton van Overbeek
Isn't it just a memory issue? 3B+ has 'only' 1GB. Pi4 probably has more (2, 4, or 8GB). Try the Pi4. My guess is it will behave better.
Just a thought. Can it be that the other end (i.e. the color management of the monitor) is playing tricks? Thinking about i.e. colord on Linux. On my Intel Macbook...
Tkinter is not supported on Wayland (default on Pi3b+, Pi4 and Pi5). You need to be running X11. On Bookworm run raspi_config, goto Advanced Settings, Select Wayland and select X11...