There are a number of supplements out there that promise to keep black horses black. I've never used one (since my horse is pretty much white) but I think one of the main ingredients in them is paprika. You do have to be careful with paprika as it could potentially test positive if you show. I believe I've also heard that a copper deficiency can contribute to a black horse fading. Of course, if your horse is already faded this year it won't darken again until he grows his coat out.
For shiny coat, you could try flaxseed, BOSS, or rice bran. It doesn't take a lot to get the shiny coat effect. I feed mine 2 oz of whole flaxseed daily, which I buy cheap at my grocery store. They also sell them in bulk at my local feed store for slightly cheaper, but it would take me forever to go through 50 lbs! For BOSS, I think you feed a similar amount, and rice bran I've heard that a cup a day will do it. Omega Horseshine is based on ground, stabliized flaxseed I believe. The main idea is to get omega-3 into your horse, but if he's on good pasture most of the day he's probably already getting plenty from the grass.
Neither of the supplements you listed are likely to help him stay dark, or help his joints.