OrionN
Moved on
This is not true. Of the various edible seaweeds that we eat, there are green species, purple (lavender) species and red species. There is Kelp which is much thicker and tougher also. I don't have time to search for the species name right now, but there is a variety of sea weed just like a variety of land leafy vegetable that we eat.The difference between the colors is that the green is roasted, the purple/red is not. The roasting is what changes the pigmentation. I have found both in the oriental market/grocery stores- just look at package carefully. Mihn, the ones I've seen are all the same species of seaweed.
You may want to read the Wikipedia page on Nori or seaweed.