I couldn't find much information online about those blennies (except for Witt's report on Bundoon blennies) so I'm reporting here what I've witnessed.
I bougth these two fishes and, as they were the only specimens of this species at the store, I did not actually chose. They were on separate tanks and looked a little different.
Fish A of slim but ate well, also its color was more bright (the white was more white, you know...).
Fish B was more rounded and more dull in color (the white body was a little more washed with shades of brown here and there).
From what I could read, females were more rounded and males looked "skinny". So my guess was A=male; B=female.
I started with the same idea of putting the two in the same tank with lots of pipes but kept an egg crate division until they looked fine to each other. This didn't took long.
Most of the time they ignored each other with some quick displays from fish A while B got frezeed with a really mottled pattern (similar to the sleeping colors of foxfaces) almost brown with dull white streeks.
Egg crate was removed after a week and displays were more frequent. Fish A out and about while fish B in the pipe. Until B took a good chunk of A's anal fin. OUCH !
From that moment on they alternate who displayed and who looked scared. The roles alternated after the scared bit the "displayer". The same goes for their colors, the dominant one become more white and the scared more brownish. They declare truce during feeding time and tolerate each other with only quick displays from both.
This has happened since then with fish B being the tank ruler most of the time.
A couple of weeks ago I noticed a color change in A. I mean, I'm quite sure that difference was not there before...
Fish A is still more submissive and still being bitten at times but is always the brightest in color. Its anal fin has developed a white color in the tips of its rays making it easily distinguished from B. And the best part is
A is tending eggs !!!
I do not know if this color difference is sexual or not but I do not have other fishes to compare I hope this can be of use and, if someone can put this color difference to test, write here !
I'll post pictures later and start a journal as well.