AAQ – black wasn’t only used to disguise one’s self; the gemara means that you should minimize the chilul Hashem if someone chas veshalom is going to sin – the black is to not stand out and be recognized, not a sign of a sinful person or even a sign of mourning/somberness (although i wouldn’t be surprised if one of the meforshim says so on this part)
If black were the color that sinful people would wear, the gemara wouldn’t say to wear it, if the point is to minimize chilul Hashem or even if it were to impress the severity of what he is about to do