Huh. Mine were the light browns, probably from MM. they laid great. Then, I also crossed them with my ee and got little hens with weird combs that laid huge light green eggs almost daily. They're still laying a few a week at I think 4&5 years old (maybe 3&4, thank you chemo-brain). Just depends, I guess. Thinking about it, the white one are the commercial strain, so they're probably better.
Aren't chickens just plain weird? You just never know with them. The two brown Leghorns in question didn't lay their first egg until they were 55 months old, either.
I do love MMM EEs, though. They lay better than any EEs from any other hatchery I've tried. They lay as well as my RSL.