I have had 2 Bi colour blennies. and 2 Algea blennies. My friend have had 3 algea blennies...
Bi colour #1: Died by jumping from the tank (atea anything and everything).
Bi colour #2: Died via whitespot in my sons tank after living happily in mine for oever a year

(Ate anything and everything).
My Algea Blenny #1: Died when it was introdiced into a tank far too young to sustain it (It only ate algea)
My Algea blenny #2: Still going strong and growing very large! Had him now over a year and its lived in both my tanks. In all this time its only ever eaten algea on the rocks and glass. (It wont even touch dried nori seaweed).
Friends Algea blenny #1: Died due to starvation (No algea)
Friends Algea blenny #2: Died due to starvation (No algea)
Friends algea blenny #3: Already looking ill when purchased and also died due to starvation (No algea)
I have a Dot Dash blenny in my tank at the moment also.. the Algea blenny eats only algea.. the dot dash will eat anything.
I can only give information on my own experiences but I stand by my statement that Algea blennies need Algea or they will stave. Bi colours or dot dash blennies can sustain on other foods.