Final answer:
The Rosetta Stone was black with white lettering. It was cleaned to reveal its original ancient material at The British Museum in 1999, while a portion was left untouched to showcase the wax and paint used in its preservation.
Step-by-step explanation:
The color of the historical Rosetta Stone was originally discovered to be black with white lettering once it was cleaned during the Cracking Codes exhibition at The British Museum in 1999. Restoration efforts involved meticulously cleaning away substances such as grease, carnauba wax, printer's ink, and white paint to reveal the original, ancient material.
A fascinating aspect of this conservation work was leaving a small untouched square at the bottom left corner showing the darkened wax and white infill for educational and preservation purposes.