True, pure Sativas are naturally a lighter green/lime green colour and that yellow leaf is just an old leaf that has served its purpose and is ready to fall off.
Having grown many landrace Sativas in my time, I can say feeding with quarter/one third/half strength (at most) fertilizers is about right and especially don't over do it with nitrogen, they just burn too easily, - especially avoid guano type fertilizers.
Ace Seeds (website) have many tips about growing landrace Sativas if you are keen for some extra input, they also breed wonderful landrace strains too!
One of my diaries has many pictures of some of their strains if you are interested.
Ace also used a lot of my pictures that I sent them for their website, so no, you are not seeing double!
Cheers, Organoman.