I wanted to avoid stains when possible because the refractive index of bare wood is 3 dimensional and complexly enjoyable. Some dyes are minimally destructive, but pigmented stains obscure quite a bit. I sought out clear finishes with maximum UV blockers and film density. Without UV or oxygen wood stays fairly fresh, and over time it mellows attractively. Around 1983 when the CS3 accelerated sales, I co-developed a custom finish with Guardsman. By modifying some chemistry we got lower levels of dangerous outgasses plus higher levels of UV protection and film density.
The only stains we used were German metal oxides and/or chemical transformations (coloring via chemical reactions with the wood).
Fast-forward to around 2018 when I bought a used pair of CS1.6s and was chagrined to find the Morado finish to be a heavily pigmented, fairly bright red coating. I learned that the Guardsman custom lacquer had been replaced by an ordinary product. Also, I have seen some seriously sun-bleached Amberwood and my Dark Cherry SCS4s are heavily pigmented.
The short answer is that before 1995, Thiel put considerable effort into keeping our wood finishes natural-looking and long-lived, but later those sensibilities and capabilities were lost. Wood has a life of its own, and resists being managed.
