When using the Samsung Good Lock Theme Park app to create custom themes, the Samsung Gallery app doesn't change it's background color in Dark mode. Instead of using the custom background color, like it does in Light mode, the background stays pure black. The Gallery app should be using the color the Android OneUI theme provides, instead, the pure black color is hard-coded in the app. This doesn't happen when using other Samsung apps such as the Settings or Clock app, they all work perfectly fine with Samsung Good Lock Theme Park themes, both in Light mode aswell as in Dark mode.
The screenshot shows the issue on a custom demo theme I created that doesn't contain the color black at all. The colors of the theme are exactly the same for the Light mode and Dark mode portions of the theme. (as shown by bottom RGB value of the pixel colorpicker.
Note that this is only the case when Android is set to Dark mode.
I am using the latest version of Theme Park, Gallery and Good Lock.