Pretty simple question. The color black I heard was at some point the same as the color white. I have a theory why this could be but is it in fact true?
This is better suited to /r/linguistics, but the gist of it is the root of the word black in Proto Indo-European (PIE) meant "shiny". The word bleach has the same root. As for how we know this, you may want to read up on PIE and historical linguistics in general. (I'm not a linguist, but I found In Search of the Indo-Europeans and Empires of the Word to be great books for the layman).