There wont be new colours per say, existing colours will just change a bit. This is not a re-paletting of the worlds, it’s an internal change to how we colour blocks so that every block has a consistent 255 colour set across the whole universe of current and future worlds. All existing worlds and inventories migrate to ‘whatever new colour is closest’.
Old way, we generated a set of 3 colours of wood, 3 colours of grass, 3 colours of rock, and other blocks colours, for a single world, and those got appended onto the limited set of colours in the palettes. But there was no re-use, and nothing to stop various colours accross worlds looking almost identical, so lots of wasted space in the colour spectrums and non-uniformities, and confusion. And because we have 3 rock per world etc in the same palette, it basicly meant we could only have 85 unique world palettes before the system would fail. It would be infeasible to give all the colours names, and because we would never have worlds with natural rocks that are super vibrant pink (for example), we’d end up with 255 rock colours that only have a limited colour range and lots of duplicates/confusion. Even worse, palettes like gleam, there is only 1 per world, so there wouldn’t even be 255 gleam colours, only 85! Urgh!
Now, we have a 255 set of colours across the entire color space in a uniform* way, that every block uses, and worlds pick out of those colours instead of adding new ones. So no duplicates or bunching up wasting spaces etc, and colorindex 5 is always the same colour on any block effectively and we will be able to give all the 255 colours sensible names too, and even support tinting/painting blocks as a game feature in future since they all will use the same colour sets.