The table you're looking for is at 08464300. It has 4-bit entries. (Firered)
EDIT: How I found this out:
As you probably know the C7-Script-Commands overwrites the color to use for the next textbox. This commands writes its argument to 020370DA. Now I put a writing breakpoint on 020370DA. 0xFF is written to this position in every frame by 080CBDF0 so I turn the writing breakpoint off and replace it with a reading breakpoint. This one triggers at 080CBE04. The code shows: If 080CBDF0 isn't 0xFF it is used as the color. Otherwise a function (0813CD24) is called to read the color out of the table mentioned above.