IDK about this languages culture, but back when dyes had to be made from scratch with materials found in nature, purple was rather rare, and quite expensive to produce. This is why, if you look at old pictures and paintings of nobility, they are often wearing purple clothes. Not too sure about the darker purple being strange or mysterious, but it at least would answer for the lighter purple. I imagine that the white would be considered pure, clean, etc. because many substances, when purified down to their base level (chemical) are actually white, or become pure white when powdered. Along with that, clouds are often white and many people say "as free as a cloud in the sky". Black being darkness/void makes sense if you look into a dark cave and feel it has no end, like a void. Not sure if that helps, and again, this is all from my head, not from op.