Yep, and... purple is being used for Harshland Conditioning alternate tech while implemented partially for the Extremes framework for Toxic(Volcano), Barren & RadioActive tiles. Violet is for Aquatic stuff such as the Abyss! Etc.
Indirectly though... since, there is a maximum of THREE default levels of Terraforming (Improvable types of Terrain, that is) in the code. I've been asking for at least two more levels to SD staff for many months - and, i won't give up.
Colonization is a different beast; right now, we're limited to a 0_50_100% process to gain extra advantages for Extremes. I'd also wish some 4th & 5th gap for that system (0,25,50,75,100) along with the all important PQ calculations of supplemental tiles for each -- as matched with the Terraforming principles above.
Making the Extremes feature, more challenging BUT, complex enough to add a strategic development asset beyond the usual Green to Y-O-R automation by choosing new surface tile "potentials".
I've always felt sufficated on many so called Paradise planets of PQ26+ where 72 are available, making 46 of 'hem wasted. Coding the above alternate system, can approximately activate a dozen+ more tiles in specific situations.
Mind you, i'd need these extra tiles **because** of the many other PIs introduced in X-Worlds and for tactical concerns beyond the SD designed gameplay balancing factors.