I had them on my last boat for fishing and nought diving.
First I used green lights which attracted fish that seemed to almost be entranced by the lights, even jelly fish were attracted.
My next boat I used blue LEDs, these also attracted fish but the behaviour was much more aggressive. Small bait fish would get smashed by bigger fish and the big fish would get smashed by seals.
We target broadbill offshore at night, where we use all kinds of led lights and flashers. The offshore stuff at night is fascinating to see, giant squid, flying fish, sharks and dolphins etc all come around for a look.