Mr. X:
... in the UK at least, reflective material is VERY EXPENSIVE & hard to buy is non-tiny, non-huge quantities. Dayglo (strontium aliminate) is cheaper -- but I think somebody mentioned that its no much good.]
I ended up getting a relatively large quantity of reflective white reflective tape off ebay (from a sign writer that had been to a trailer company's bankrupcy sale in Scandinavia!). I marked up all my gear will it. It looks ok.
Also, it works -- I dropped my dive knife (again!) while removing the spear from a speared fish but quickly located it on a nearby reef -- the band of reflective tape around the handle made the hard-to-see black and grey knife standout clearly. I also
dropped my clear snorkel as I entered the water, at first I thought I had forgotten it but decided to feel around -- the 2"' of white tape I added to the tip help locate it -- but a different colour and larger marked area would have help [BTW my next snorkel will not be clear (will prob. go for black) and will not have a valve (unreliable, waste of time) but will have an orange tip (much safer & easier to see) and (preferrably) a 2 slash semi-dry top (a simple improvement that does seem to work without hinderance)].
The tape held well except for my old black fins, on which I used a lot of tape.
I added diagonal stripes to the fins and solid blocks around the heels and squares inside and under foot. They looked rather cool. However, after a week solid of spearfishing from beaches & on reefs, about a quarter of the tape has now come off or is peeling off the fins -- which is a tatty. However, most is still on. I have just bought some new fins (a surprise find, a nice pair of Speedo fins from JJ Sports a UK chain store -- quite large, sleek, full foot pocket (ideal for snorkelling), blue & black plastic/rudder and in a decent nice mesh bag and at 14.99 GBP a v. good price by UK standards) and plan to mark those up, as I still have a lot of reflective tape left ... probably just a few large blocks or stripes (to maximize hold), as smaller pieces come off easiest.