Gosh, isn't this a bustling thread!
Concerning seeds, Eclectus don't process fats as well as toos', greys, teils', etc, as they are frugivores (fruit eaters). Their digestive tracts have evolved to cope with high sugar-content foods a lot better than us, so we can't view their diet like we would our own.
(My vet is a world expert on Eclectus - Dr Rob Marshall. So I trust his years of research)
A few seeds is ok, but they should be used as treats ONLY. Same goes for nuts. Protein is more necessary for females than males (but that correlates to the egg-laying), very young birds and those breeding. So a little animal protein once a week is fine, but the incomplete protein sourced from legumes is all that is really necessary for them (taking the above consideration into account).
A normal amount of food to be eating is 80-120g per meal (depending on sub-type, age, size, etc) on a two-meal-per-day routine, but really you'll know how much to feed based on what get's literally spat back at you
Honestly, they take so long to feed so making up a batch in bulk (enough for a week or two) is essential to YOUR health! I make up a batch combining rice, mixed beans (soaked over night), broccoli, zucchini, carrot, pumpkin, sweet potato (extra vitamin-A is vital for eclectus, as in a considerable amount more than other species), quinoa, apple, strawberry, passionfruit, peas and some chilli. Poe LOVES this mix, and all I have to do is thaw out a baggy each day and heat it up a little.
(I'm not a morning person due to late shifts, so heat-and-stir is all I am capable of before my coffee and with a squawky-little-**** on my shoulder who fails to respect the need for silence first thing in the morning... the little darling.)
As for the dark feathers, Poe still has some dark patches on his that the vet said were stress-bands that can occur during weaning. It doesn't necessarily mean that the bird was rushed, as I was still hand feeding Poe when he arrived at 10 weeks old, and still spoon-feed his breakfast when he wants me too), but just that he found the experience, well, stressful. I imagine some birds may have larger/darker bands that would give the appearance of patchiness. Especially if he's been in for a health-check and has come back clean, this would fit the diagnosis.
He's a very talkative bird, he has little screaming moments but that's usually at our tea time and he is wondering why he isn't getting any of what I'm eating. He's 19months old so not reached the maturity age yet so I can't comment on any behaviour changes from that. 
