Since my last post on the topic of smoke colors a few weeks ago, I've expanded my catalog of smoke colors quite a bit.
After sharing some initial observations with my Canonn friends, they pointed out that smoke colors match the colors of the material nodes (I'm still kicking myself for not having noticed that much earlier). So I've been able to use the colors of the material nodes and soot to help identify the real color of the smoke in a given site.
After visiting two or three hundred Geological sites, I've found that there are at least 17 different smoke and material colors, namely 3 shades of Grey and 4 shades of Green. There are 22 different types of Geological sites listed in the Codex, so together with the 17 different smoke colors there are (so far) a total of 374 different possible site-color combinations. As of the time of this writing, I've seen 89 site-color combinations, as shown in the table below.
One of the surprising things I've found is that, when it comes to non-Icy bodies (HMC, RB, and MR), there is no such thing as purely White smoke, only shades of Grey, which ironically can make the smoke look "whiter". There is a preponderance of Grey shades and Light Green on non-Icy bodies. Other colors, such as Red and Purple, can be hard to find. White smoke on Icy bodies is accompanied by Black colored material nodes, which is somewhat counter-intuitive but I suppose a purely white/transparent mat color doesn't look as good from an aesthetic viewpoint.
The images below are a collection of Cristalline Fragments of various colors that I use as a reference to help me identify the exact smoke color of a site. I have a similar catalog of Cristalline Cluster, Piceous Cobble, and Soot.
For the purposes of identifying smoke colors, I limit myself to the day side of a planet. I prefer planets that are not too far away and not too close to the star. The sweet spot usually happens at around 2000Ls in F-class star systems, where the colors stand out nicely and are not washed out by the starlight.
It'll take a very long time to fill the entire grid, but I'm taking my time and just treating it as part of my "personal narrative". Hunting for specific colors and rare Volcanism types (i.e. Nitrogen and Methane) adds spice to exploration trips =)