You have to consider that we will be getting a new tier of rare resources above gems at some point in the future. @Jiivita already found some in his video on the hunting worlds.
There will be 255 colors for each block, so as long as we don’t get 255 planets with no overlap, some colors will be rare or unobtainable. The devs teased some possibilities to transfer colors between blocks to create block-color combinations that don’t naturally occur in the universe. I assue this process will be expansive, so I guess these blocks will be quite rare and very interesting for the economy.