There’s more out there. Gem planets (stated by james) have the most chance of generating colors far out of palette, as I think @bucfanpaka mentioned. I can confirm that with high confidence but also some of the threads about this were hundreds or thousands of posts, it’s super hard to find quotes on this.
Regarding the original files posted above, someone analyzed that and said black gleam was actually blocked despite what James said. A couple of days later there was a black gleam sov, so I have no idea if that’s bad analysis, or shenanigans on the part of the devs.
They actually did this, and it sucked. They changed it early on. Each world type starts with a palette/range based on type and tier, then randomizes based on those biases.