There are some machines that are what we call "black side" in that they have blacken surfaces instead of chromed. Some say it was an effort to cut costs during WW2, but I don't know if that is true or not.
Usually it's the needle and slide plate, and sometimes other parts. Singer simply put those parts on as they used up the old stock, so you'll find an assortment of combinations on machines. It was more often with crinkle finishes, but again, it was a time frame issue. Attachments were also made "black side" at the time, and some have a mix of black and chrome - quite interesting to watch for. I don't recall seeing a 201 with any blackside parts, I've seen several 66's and 128's that have them.