A lot has been said on this topic. Here are my thoughts on how a Meerschaum colors
1. Meerschaum is super absorbent - So it is logical it should color from both inside and outside
2. Coloring from outside is obstructed by the wax - which acts as a partial barrier
3. The tobacco and the carbon build up also acts as a partial obstruction for coloring from inside
4. Point 2 and 3 above explains why the shank colors first - It is the place with least amount of obstruction
5. Point 2 and 3 also explains why condorlover’s coloring disk and coloring bowls work - They create an air pocket where carbon does not build up and tobacco is not there to obstruct the absorption
6. Internal airway would absorb most of the tar condensation- While meerschaum also colors from outside the amount absorbed is extremely small
7. Collected tars are liquids and it would move in the lattice through capillary action. This movement is extremely slow
8. Capillary movement would also be across a thermal gradient due to changes in surface tension. This would explain partially colored meerschaum losing color when not smoked for some time. The rate of movement across a thermal gradient is faster than a normal movement. This is also where my conjecture/theory is weak.
9. Points 6, 7, 8 above along with the fact that bowl absorbs least amount of tar (Also explained above) why the bowl colors extremely slowly
10. Beeswax by itself I don’t think discolors, but it is a possibility beeswax can absorb tar as well and get colored
11. There was a science teacher who was a member here - He had a theory that wax changes the refractive properties of the surface, making it brighter. That is an extremely plausible theory and can explain some of the initial color of the stem
12. I have a stone ashtray which would collect tars (Which it cannot absorb) - The tar is deep brown in color - This color mixed with the pristine white of the meerschaum would also explain all the stages of meerschaum colors - Pale yellow to deep plummy black based on how much tar the meerschaum has absorbed
13. If you see the cut section of Chasing Embers pipe - It is clear it has absorbed some tar from the surface - The surface color is a couple of mm thick