I've previously had some Vic Haps with those 'black dots / streaks' you mentioned. Agreed, they don't go away ... and they
don't spread either.
I've tried various meds, but they didn't seem to work. I was once told it could be 'acid' marks or 'fighting' marks, but they were never confirmed. It is important to note that the fish looks healthy, eats well, and even fights well all the time.
I still have a Electric Blue which has some 'black dots' on him, but when he colours up you can't see the black marks at all. The fish is doing well, eating well, and trying to mate with the female (with no luck still).
If I had to guess - these "Black Dots" could be signs of decay due to external and/or internal parasites. Don't take my word for it though.
To be safe (& spend some money) - get some of those "Ocean Free" meds (or other brands if you prefer) ... treat for External Parasites for one week (ie. one dosage followed by another dosage after 3 days, then a 50% water change after seven days). Then treat for External Bacteria (again, 1 dosage, 1 more dosage after three days, then a 50% water change after seven days). Finally treat for Internal bacteria (1 dosage, 1 more dosage after three days, then a 50% water change after seven days). You can also choose to treat for Internal Parasites after that.
The "Black Dots" disease (forgot the actual term) don't usually affect freshwater fish - it's more of a marine fish disease. I've yet to see it personally (touch wood).
Good luck!