Not at all, my gun is bright red, my float line is made from clear PVC tubing which reflects light like a mirror (and I'm a camo freak rofl) either the fish I shoot are daft or they don't give a damn
I'm told red looks black to most fish - so perhaps your rope looks "bright black" to them. You might have stumbled onto one of the best camo float line colours.
I tried several different float lines over the summer, including bright yellow braided polypopylene (around 5mm), 3-strand blue poly rope (6/7mm?) and camo 4mm parachute cord but ended up going back to my original, inexpensive Rob Allen Olive green polypropylene float line (would prob. be good as a kayak anchor rope too), which I now keep half coiled on a winder. [I originally ordered the hi-viz orange version, which they also sell, but glad now that they suggested olive.]
The para-cord & blue rope were too soft & tangly. I did not see/spear many fish while using the stiffer yellow poly and I got a feeling it made my presence made too obvious in the murkey green water, so I stopped using it. It certainly did not attract bass in for me. I also found it distracting (conversely, I have orange spearline now which I quite like, it tends to draw your eye along the barrel & have speared many fish since fitting it, many drawn in on aspetto - so not too foreboding for fish).
For shore diving, I'll stick with a drab coloured float line, used with a big, brightly coloured dive float for the boats to see. If you're diving from a boat though or in kelp with a float line but no float, I would certainly pay attention to Bill's advice (inc. having a bright coloured tip on your snorkel). Jimbo's combination of lines is interesting idea - but there is much to be said for simplicity too
Spaghetti, what size mono do you use? I found bright rope too obtrusive but I'd be concerned that fishing line would be near invisible & that it would be hard to untangle & prone to cut on rocks. (Foxfish, although I suggested washing line previously - I've yet to find one that I like, some have steel wire cores, others sink, etc. Perhaps not wanting to spend more than 99p on it has something to do with it
).