Yes you could make marcher style costume in navarr green and browns and it would work. You would probably want to add more decoration, and the type of material you could use can be wider.
Although actually re-enactment style marcher clothing designs are more complicated than the layered t-tunic style from above so you may be adding unnecessary complexity if you’re an inexperienced sewer.
Navarr is actually one of the nations, along with the brass coast which could be costumed entirely from charity shop hunting, with very little modification if wanted. Leggings, a couple of long tops, a belt and a mock suede / leather jacket would work fine if you can find suitable items.