YES, if they don't lay a minimum of a "4"on the Marans Egg Color chart, they are not considered a Marans. That said, per DMR below, it's not an SOP requirement, so judging a Marans, just like judging other colored egg layers such as Ameraucanas or Welsummers, is based soley on type.
I disagree about getting dark egg color back; it's not an easy task, IMO. There is very little research that's been done on the genetics of egg color. It's been said that you can lose egg color if you breed a different line into your existing one, but I have not found this to be true. Just my own personal experience, though.
I personally DO believe you can have both - I certainly do! My birds (and birds hatched from my line) have won reserve and champion Continental titles...and I have also won many egg shows. Not to toot my own horn, in fact, I'm extremely uncomfortable about that, but - wanted to share my observations. I WILL say that for me, type is the most important. Once I was satisfied with the egg color I was seeing, I began culling for type. I definitely do not see "9" eggs in my nest boxes, and only very rarely see a true "8" either, but most definitely, my hens average a 6/7 at their prime.
With my line, good males are few & far between, unfortunately. I'm working hard to not have to have separate male/female lines. However, when a really nice male comes along, they are VERY very nice. They're just not coming along often enough in this line! I'm hoping to improve on that as I move forward.