Sometimes when loading or unloading a resource pack, residues of the default/previous resource pack can still be seen on the UI.

It can sometimes be in the inventory, sometimes in the chat, in the menus, or in the main menu.

It seems to affect some items too

This bug mostly only happens the first time one loads the pack, if you unload it and then load it again most times it fixes itself.

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Edit by Magdalena Wardak

Adding reproducible steps provided by @Skaijie:

Steps to reproduce

1. Load a world and check the colour of the inventory tabs in Survival
2. Install and load MCPE-66773_darkmode.mcpack to the ticket (original download site)
3. Load a world and verify the inventory tabs are now in dark mode
4. Close the world and restart the game
5. Enter the world settings and tick the "Require players to accept..." option under Resource packs, ensuring there are no other resource packs other than the global resources default
6. Click Play
7. Check the colour of the inventory tabs again
   →  The tabs are still in dark mode when selected

There may be other ways to reproduce. Reproduction performed on Windows 10