I'm sorry to tell you this but your neighbor's feed is the one that sucks. It is NOT chicken feed. He is simply feeding scratch grains that are devoid of many of the essential amino acids as well as vitamins and minerals. Purina Layena is not only far superior to the scratch grains your neighbor is feeding but is one of the better feeds on the market. Scratch grains are nothing more than cracked corn and a few other seeds and grains mixed in and in no special ratio.
Companies that make scratch grains will change up the mix and percentages based on what is cheapest and most available at the time. A complete poultry feed, on the other hand is based on well over a century of research into the precise nutrient level needs of various poultry.
You can tell what kind of foods a bird has evolved to eat based on the shape of its beak. Birds with hooked beaks are birds of prey for ripping apart meat. Chisel-like beaks as in woodpeckers are for drilling into wood. Birds with conical beaks, like sparrows are seed eaters. Chickens are not seed eaters. They have pointed beaks for digging into soil for worms and insects. They will also eat fruits, vegetation and seeds but most importantly, they are omnivores and expecting them to subsist on seeds alone is ignoring their nutritional needs.
Let me explain how this "processed crap purina stuff" is made and why. Primary ingredients like grains and legumes are assayed when they come into the mill by train for amino acid, vitamin and mineral levels and then the other nutrients chickens need are added at the proper ratio to make up for what is missing in those primary ingredients. A binding agent is added and all are thoroughly mixed with the hammermill ground grains and cooked legumes, steamed, run through a pelletizer so that virtually every bite of feed contains all the nutrients needed to optimize health and productivity. If crumbles are desired, the pellets are run through a crumbler. It contains the same nutrition - bite after bite. If mash feed is made, the feed is more finely ground, no biding agent is added and the run down the pelletizer line is skipped.
When I worked at a facility in Central America with over 400 Scarlet and Great Green Macaws, the biologists and I wished we could afford "that processed crap purina stuff" but all we could afford were 'past their prime' fruits, vegetables, root crops from the local market plus rice and beans. Then after we cut them up and mixed them, we would apply a vitamin and mineral supplement mix. It would have been more appropriate and easier to provide a pelleted macaw food, likely made by Purina due to their decades of research into the dietary needs of most captive and domesticated species on the planet.
Scratch grains should make up no more than 5-10% of the diet with a complete feed like Layena as the primary food.
Assessing the quality of feed by the color of resulting yolks is misguided at best. What you are seeing in the yolk is the result of various yellow, orange and red carotenoids consumed by the hens such as lutein, zeaxanthin, and canthaxanthin, Chickens don't assimilate carotenoids so they end up in the yolks. The color of the yolk doesn't reflect on the quality of feed.
The primary ingredient in chicken feed is yellow corn. Yellow maize contains several carotenoids including xanthophylls. This is what makes yolks yellow in parts of the world where yellow corn is used. In much of Africa, white corn is the primary ingredient resulting in yolks that are almost white. This doesn't mean that the feed is inferior or that the eggs are less nutritious.
Your neighbors' egg yolks are likely darker because scratch grains will have a higher percentage of corn than chicken feed. However, if your neighbor continues to feed scratch grains and no real food, eventually his birds will cease laying (from the lack of protein) and start suffering from a variety of nutritional deficiencies. The first to be noticed are those from water soluble vitamins and mineral deficiency, then eventually to the fat soluble vitamins because they are stored in the body longer.
Some other foods that contain carotenoids are cantaloupe, mangoes, papaya, carrots, sweet potatoes, spinach, kale, pumpkin, alfalfa, watermelons, tomatoes, guavas, asparagus, red cabbage, red bell peppers and parsley.