What I can see in the EPC is this:
Ivory coloured knob is PN A1112680742
It is not on any W113 part list.
It is for W110 and W111 and it is only for manual transmission. I guess in w110 and W111 if it were automatic, it would be the steering wheel gear shift, so perhaps the ivory one did not exist for automatic version of floor gear shift. For shifter at the steering wheel in these cars there is an ivory option with a not (001) ON SPECIAL REQUEST
For the manual transmission the only note I found was for 110.116, saying: (053) ON SPECIAL REQUEST.
The only special knob I found for W113 is the one for ZF gear box.
If this option was not on the price list for W113, I would have thought it is likely that if a customer was ordering ivory steering wheel, the dealer would suggest ivory knob for manual transmission too. Logical trade up.
But all this may be wrong. Maybe at the factory they were fitting ivory knob based on some internal instructions. It would be good to look at the paper parts lists or price lists where options were listed - perhaps they mention it in the code for ivory steering wheel description.