Phoebus: Yeah, I know or understand what you mean with unique and natural.... and so am I moding those colours to match those stones I encountered in the field and... well.... one of my fav-types in real life is
Labradorite... I like your choice for rhyolith/rhyolite as it matches the picture from the german wikipedia - and so I just like 'em to keep the colours to those I know from own experience and local occurence (and at least for granite or such that is really many variances for us here in Berlin, because we have so many pebbles and "Findlinge" in our glazial sediments of various origin (Oops, there is no english wikipedia article for "Schriftgranit" and even the german one is just a placebo... but that type of granite, as the general one, can be of white/gray, redish or whatsoever colour (fieldspar component, see below "*"))... but in general I tend to set the ignious/plutonic (and ok, nowadays it is not used for them anymore - extrusive) rocks to colours alike to their mafic or felsic state in regards to the QAPF Diagram (for extrusive ones the current diagram used would be the TAS one).... just asked because I am new to meddle with anything besides personality (.28 times) and now also attribute value for new embarks (temporary change for just the embark) and don't wanted to mess up the whole graphic set.
P.S.: And I really would wish that background and foreground colours would be more consistend (and possibly extended for variances) in game - alone the colours fieldspars may have.... and then there would be the point of withered appearance compared to polish one (crying out loud at least two colour designations - untampered and tampered with) - simply observable with granite - in general it is more light/grayish in handsample and darkens with a smoothed surface as the Mica minerals become more observable/aren't tarnished anymore ("*" Btw.: Old Proverb for us geology students for granite: Feldspat, Quarz und Glimmer - diese 3 vergess' ich nimmer (nie mehr) [Fieldspar, Quartz and Mica - those 3 I will not forget anymore])
P.P.S.: Wonderful update!