I am at risk of repeating myself, but the key issue in being seen is awareness. This is massively the responsibility of operators of powered vehicles, or at least used to be. I recall a public safety advert (or I think I do - getting old!) that showed a "good driver" noticing a kid's feet behind a parked car and expecting that child to run into the road. That sort of notion of responsibility seems to have gone - replaced by a Clarksonist sense of entitlement to tear about at high speed all the time and mow down whatever is in the way.
Nevertheless, a rider needs awareness too. Part of a regular ride I do involves a stretch of single-carriageway high-speed road (which I hate, but can't avoid). Early in the morning, with low sun, a rider is almost invisible in the deep shadow of the high hedge. Thus, I ride on the lit part of the road - yes, the middle - moving over only when I am sure the overtaking vehicle has seen me. Surprisingly, I rarely get hooted for this, but at least a hoot means I have been seen.
One last thought about colours. Industrial high-viz is designed to stand out in an urban, man-made environment. Most of the background to my personal riding (my choice) is nature or agriculture. Yellow clothing does not work for me when I am riding past oilseed rape, or even spring green leaves. For this reason, I mostly wear black and white. It might be interesting to consider the journey made by the RAF when choosing a colour to make their training aircraft as visible as possible in the natural environment. They have moved from yellow (1930s and 40s) to orange 1950s and 60s, and now use black.