Pea comb doesn't do anything for the blue eggs, the linkage only exists because by coincidence the two separate genes happen to be located very close together on the same chromosome so they strongly tend to inherit together. They can inherit separately on occasion with the result either being a pea combed lacking the blue egg gene or vice versa.
The pro to using the blue egg- pea comb linkage are in programs where one wants the pea combs.. colored egg pullets can be selected as soon as they hatch or are identifiable as to their sex by comb type- simply pick and keep the pea combed ones as those have a 90+ chance of laying colored or in this case, olive eggs Using legbars or any single combed colored egg layer onto Marans. you don't have that option, have to raise all pullets until laying age and then identifying which ones lay olive eggs or not. But the egg color ranges will be the same.