Not sure i would treat unless you know what your treating for. Sounds like a healthy Blennie to me. The flashing would be a sign of problems but like you said its sometimes which i take to mean not very often. Usually fish do this quite often if there is a problem. Usually with flashing also you will see some outward sign of a problem.
29g Mixed Reef, 150w 14k Phoenix MH w/ Moonlights, Reef Octopus BH1000 HOB Skimmer, Ecotech Vortech MP10es, ReefKeeper Lite (Plus), PH Probe, Temp Probe, ATO, Carbon/GFO Reactor.