Black nylon coated strings usually are lower tension. Sometimes they are rounds with the nylon coat over them. Others are flats with the same. I have wanted to like these strings but I just can't settle with them.
Thomastik Jazz Flats are lower tension and lovely, IMHO. I come back to these strings again and again. I find they don't suit every bass I have. I have them on my ACG at the moment and they sound great on that, probably due to the heavy woods involved. Lovely big fat tone. Didn't sound so good to my ear on my Cort which is Agathis and much lighter.