Depends on the light levels and the location tbh.To you they are. To others maybe not.
Cyclists in High Vis disappear on country lanes as they blend into the background easier than a contrasting colour during the Summer and parts of Spring/Autumn.
Wearing absolutely plain black with very dark backgrounds would have the same effect, but where do you cycle where the background is black?
As it gets darker, the colours come into play again, but then a set of good lights covers that.
Personally, I wear black, but my Winter gear has reflective bits on front and back. I think that is more important than the colour, if anything.
Much like the uniform of a Fireman is predominantly dark with reflective elements.