The palette per block is finite at 255 colours, as we need to efficiently pack the blocks in the voxel chunks. So players will have 255 colours per block to play with. (Which is actually a lot!) But the combination of block colours selected per world is huge. So yes - ultimately there will be multiple worlds with (say) Red Gleam, but no - there should not be 2 worlds with the same final palette.
More interestingly from a gameplay perspective, with a shared palette ordering per block (Red Gleam is the same index as Red Rock) there might be some block colours that don’t get procedurally used during generation. So players would only be able to use these by (some future) dying process.
The non-block colours (time of day sky gradients, sun / night-sun, etc) can be selected uniquely per world as they can’t be transferred, so we can use absolute values rather than a predetermined palette.
The Sandbox will need expanding … slightly.